Help

<?php
session_start();
if(!isset($_SESSION['username'])){
header("location: index.php");
echo "<script>alert('Anda belum login mas bro')</script>";
}
?>
<html>
<head>
<link rel="shortcut icon" href="keys.ico">
<title>Login sebagai : <?php echo $_SESSION['username'];?> </title>
<meta name="author" content="RieqyNS13">
<meta name="description" content="Upload by RieqyNS13">
<meta name="copyright" content="Copyright &copy rieqyns13@hackermail.com">
<meta http-equiv="Content-type" content="text/html;UTF-8">
<style type="text/css">
body{
background-color:#000;
color:#00FF00;
font-weight:bold;
font-family:"Courier New";
font-size:15px;
}
input{
background-color:#000;
color:#00FF00;
font-family:"Courier New";
font-size:11px;
}
</style>
</head>
<body>
<form enctype="multipart/form-data" action="<?php $_SERVER['PHP_SELF']; ?>" method=POST>
Pilih file mas bro<input type="file" name="file_upload"><br>
<input type="submit" name="btnSubmit" value="Upload mas bro">
</form>
</body>
</html>
<?php
if(isset($_POST['btnSubmit'])){
if(!empty($_FILES['file_upload']['name'])){
if($_FILES['file_upload']['error'] >=1){
echo "Error Mas Bro - >". "<font color=#FF0000>".$_FILES['file_upload']['error']."</font>";
}else{
$target = "files/";
$name = $_FILES['file_upload']['name'];
$type = $_FILES['file_upload']['type'];
$size = $_FILES['file_upload']['size'];
$tmp = $_FILES['file_upload']['tmp_name'];
echo "Name   : ".$name."<br>";
echo "Type   : ".$type."<br>";
echo "Size   : ".$size. " byte <br>";
echo "Tmp_name : ".$tmp. "<br>";
echo "Target : ".$target.$name;
///\\\\\
if(file_exists($target.$name)){
echo "<script>alert('$target$name sudah ada mas bro')</script>";
}else{
move_uploaded_file($tmp, $target.$name);
}
////\\\\\
}}else{
echo "File belum dipilih mas bro";
}
}
?>