My reg form

<?php
session_start();

//connect to database
$host = 'localhost';
$user = 'root';
$password = '';
$name = 'registration';

$db = mysqli_connect($host, $user, $password, $name);
	if (isset($_POST['submit_btn'])) {
		$username = mysqli_real_escape_string()($_POST['username']);
		$email = mysqli_real_escape_string($_POST['email']);
		$password = mysqli_real_escape_string($_POST['password']);
		$password_again = mysqli_real_escape_string($_POST['password_again']);

		if ($password==$password_again) {

			//create user.....
			$password = md5($password); //hash paassword for security reasons

			$sql = "INSERT INTO users(username, email, password) VALUES('$username', '$email', '$password')";
			mysqli_query($db, $sql);
			$_SESSION['message'] = "You are now logged in";
			$_SESSION['username'] = $username;
			header ("location: home.php");
		} else {
			$_SESSION['message'] = "Password do not match";
		}
	}
?>
<html>
<head>
	<title>::Registration Page</title>
	<h1 style="text-align: center;">Registration Form</h1>
</head>
<body>
	<form action="index.php" method="POST">
		<label>Username</label><br> 	<input type="text" name="username"><br>
		<label>Email</label><br>		<input type="text" name="email"><br>
		<label>Password</label><br>		<input type="text" name="password"><br>
		<label>Verify Password</label><br><input type="text" name="password_again"><br>
		<input type="submit" value="Register" name="submit_btn">
	</form>
</body>
</html>