PHP Form, validate in same page

<?php
	if($_POST['formSubmit'] == "Submit")
    {
		$errorMessage = "";

		if(empty($_POST['agreeName']))
        {
			$errorMessage .= "<li>You forgot to sign the release.</li>";
		}

		if(empty($_POST['last_name']))
        {
			$errorMessage .= "<li>You forgot to enter your a last name!</li>";
		}

		if(empty($_POST['first_name']))
        {
			$errorMessage .= "<li>You forgot to enter your first name!</li>";
		}

		if(empty($_POST['age']))
        {
			$errorMessage .= "<li>You forgot to enter your age.</li>";
		}

		if(empty($_POST['gender']))
        {
			$errorMessage .= "<li>You forgot to enter your gender.</li>";
		}

		if(empty($_POST['phone']))
        {
			$errorMessage .= "<li>You forgot to enter your phone number.</li>";
		}

		if(empty($_POST['email']))
        {
			$errorMessage .= "<li>You forgot to enter an email!</li>";
		}

		if(empty($_POST['street_no']))
        {
			$errorMessage .= "<li>You need to enter the address where you currently reside.</li>";
		}

		if(empty($_POST['city']))
        {
			$errorMessage .= "<li>You need to enter the city where you currently reside.</li>";
		}

		if(empty($_POST['state']))
        {
			$errorMessage .= "<li>You need to enter the state where you currently reside.</li>";
		}

		if(empty($_POST['zip']))
        {
			$errorMessage .= "<li>You need to enter your zipcode.</li>";
		}

		if(empty($_POST['attended']))
        {
			$errorMessage .= "<li>Please answer the question: Have you attended...</li>";
		}

		if(empty($_POST['volbefore']))
        {
			$errorMessage .= "<li>Please answer the question: Have you volunteered...</li>";
		}

		if(empty($_POST['volbeforeyes']))
        {
			$errorMessage .= "<li>Please answer the question: If you have volunteered...</li>";
		}


		if(empty($_POST['cpr']))
        {
			$errorMessage .= "<li>Please answer the question: Are you CPR certified?</li>";
		}

		if(empty($_POST['tabc']))
        {
			$errorMessage .= "<li>Please answer the question: Are you TABC certified?</li>";
		}

		if(empty($_POST['skills']))
        {
			$errorMessage .= "<li>Please answer the question: What are your skills?</li>";
		}

		if(empty($_POST['avail']))
        {
			$errorMessage .= "<li>Please answer the question: What is your availability?</li>";
		}


		if(empty($_POST['shirt']))
        {
			$errorMessage .= "<li>Please tell us your shirt size.</li>";
		}




    $agreeName = $_POST['agreeName'];
	$last_name = $_POST['last_name'];
	$first_name = $_POST['first_name'];
	$age = $_POST['age'];
	$gender = $_POST['gender'];
	$phone = $_POST['phone'];
	$email = $_POST['email'];
	$facebook = $_POST['facebook'];
	$street_no = $_POST['street_no'];
	$city = $_POST['city'];
	$state = $_POST['state'];
	$zip = $_POST['zip'];
	$attended = $_POST['attended'];
	$volbefore = $_POST['volbefore'];
	$volbeforeyes = $_POST['volbeforeyes'];
	$cpr = $_POST['cpr'];
	$tabc = $_POST['tabc'];
	$skills = $_POST['skills'];
	$avail = $_POST['avail'];
	$shirt = $_POST['shirt'];

		if(empty($errorMessage))
        {


			$db = mysql_connect("host", "DBNAME", "pword");
			if(!$db) die("Error connecting to MySQL database.");
			mysql_select_db("DBNAME" ,$db);

				function checkEmail($email) {
    $email = mysql_real_escape_string($email);

    $sql = mysql_query("SELECT * FROM vols2012 WHERE email='$email'");

    if (mysql_num_rows($sql) == 0) {
        return true;
    }

    return false;
}

if (checkEmail($_POST['email'])) {
    // Continue insert
} else {die( "There is already a user with that email!" ) ;
   }//end if




			$sql = "INSERT INTO vols2012 (agreeName, last_name, first_name, age, gender, phone, email, facebook, street_no, city, state, zip, attended, volbefore, volbeforeyes, cpr, tabc, skills, avail, shirt)

VALUES (".

							PrepSQL($agreeName) . ", " .
							PrepSQL($last_name) . ", " .
							PrepSQL($first_name) . ", " .
							PrepSQL($age) . ", " .
							PrepSQL($gender) . ", " .
							PrepSQL($phone) . ", " .
							PrepSQL($email) . ", " .
							PrepSQL($facebook) . ", " .
							PrepSQL($street_no) . ", " .
							PrepSQL($city) . ", " .
							PrepSQL($state) . ", " .
							PrepSQL($zip) . ", " .
							PrepSQL($attended) . ", " .
							PrepSQL($volbefore) . ", " .
							PrepSQL($volbeforeyes) . ", " .
							PrepSQL($cpr) . ", " .
							PrepSQL($tabc) . ", " .
							PrepSQL($skills) . ", " .
							PrepSQL($avail) . ", " .
							PrepSQL($shirt) . ")";

			mysql_query($sql);
			header("Location: volthankyou.php");
			exit();
		}
	}



    // function: PrepSQL()
    // use stripslashes and mysql_real_escape_string PHP functions
    // to sanitize a string for use in an SQL query
    //
    // also puts single quotes around the string
    //
    function PrepSQL($value)
    {
        // Stripslashes
        if(get_magic_quotes_gpc())
        {
            $value = stripslashes($value);
        }

        // Quote
        $value = "'" . mysql_real_escape_string($value) . "'";

        return($value);
    }
?>

<!DOCTYPE html>
<html>
<head>
  <meta http-equiv="content-type" content="text/html; charset=UTF-8">

</head>




<body>

             <!-- Form Left start -->



<?php
		    if(!empty($errorMessage))
		    {
			    echo("<p>There was an error with your form:</p>\n");
			    echo("<ul>" . $errorMessage . "</ul>\n");
            }
        ?>

		<form action="<?php echo htmlentities($_SERVER['PHP_SELF']); ?>" method="post">


        <div  id="volApp"  class="form_left">


<fieldset>
 <br /> <br />

<label>First name<br /><input type="text" name="first_name" placeholder="Contact First Name" value="<?=$first_name;?>" /></label>

<label>Last name<br /><input type="text" name="last_name" placeholder="Contact Last Name" value="<?=$last_name;?>" /></label>

Age <input style="height: 10px; margin-right: 12px; width: 18px" type="text" name="age" value="<?=$age;?>" /> Gender <input type="radio" name="gender" value="female">F <input type="radio" name="gender" value="male"  checked>M
<br />
<label>Contact phone<br /><input type="text" name="phone" placeholder="xxx-xxx-xxxx" value="<?=$phone;?>" /></label>

<label>Email<br /><input type="email" name="email" placeholder="Email Address" value="<?=$email;?>" /></label>

<label>Street<br /><input type="text" name="street_no" placeholder="Mailing Address" value="<?=$street_no;?>" /></textarea></label>

<label>City<br /><input type="text" name="city" placeholder="City" value="<?=$city;?>" /></label>

<label>State<br /><input type="text" name="state" placeholder="State" value="<?=$state;?>" /></label>

<label>Zip<br /><input type="text" name="zip" placeholder="Zipcode" value="<?=$zip;?>" /></label>

<label>Have you volunteered for the fest before?
<input type="radio" name="volbefore" value="yes">YES
<input type="radio" name="volbefore" value="no" checked>NO<br/ >
</label>

<label>If no, have you attended the fest as a guest?
<input type="radio" name="attended" value="yes">YES
<input type="radio" name="attended" value="no" checked>NO<br/ >
</label>


<label>If yes, what year(s), shifts/positions did you cover?<br/ >
<textarea placeholder="Ex. 2010, 2011, Sat. pm/Sun. am, wristbander, first aid, booth" name="volbeforeyes" id="bigarea" value="<?=$volbeforeyes;?>" /></textarea></label>

<label>Are you TABC certified?
<input type="radio" name="tabc" value="yes">YES
<input type="radio" name="tabc" value="no" checked>NO<br/ >
</label>

<label>Are you CPR certified?
<input type="radio" name="cpr" value="yes">YES
<input type="radio" name="cpr" value="no" checked>NO<br/ >
</label>

<label>List skills you have that can be put to good use at the fest.<br/ >
<textarea placeholder="Ex. CPR, strong, math, loud, can't stop/won't stop (No photographers please)" name="skills"  id="bigarea" value="<?= $skills;?>" /></textarea></label>

<label>A.M. shifts run from around 9am to 4pm and P.M. shifts from 3:30pm to around 11pm. While it's a ways off, do you currently know of any restrictions to your schedule that would prevent you from being available for any of these shifts?<br/ >
<textarea placeholder="Ex.: NOPE, All yours!,  Yes- Graduation Sat A.M." name="avail"  id="bigarea" value="<?= $avail;?>" /></textarea></label>

<label>What's your name on Facebook?<br />
<input type="text" name="facebook"  value="<?= $facebook;?>" /> </label>

<label>T-SHIRT SIZE
<input type="radio" name="shirt" value="small" checked>S
<input type="radio" name="shirt" value="medium"> M
<input type="radio" name="shirt" value="large" >L
<input type="radio" name="shirt" value="XL"> XL
<input type="radio" name="shirt" value="XXL"> XXL
</label>


<br /><br />

</fieldset>
</div>


 		<!-- Form Left end -->
        <!-- Form Right start -->

 <div class="form_right">


   <fieldset>

<div id="release">

<h2 class="bigboldfont">RELEASE</h2>

<label>First and Last name <input style="width:230px; margin-top:10px" type="text" name="agreeName" value="<?=$agreeName;?>" /></label>

</div>



<div style="height:60px">

<div id="verQ"><label>Spam verification: 3+1= <input type="text" name="hii"  placeholder="?"></label></div>


<input class="float-right btnSubmit" type="submit" value="Submit" name="formSubmit" id="submit">



</div>

</fieldset>
</div>



</form>

</body>
</html>