My download.php script sends a corrupt file - php

Question

I am having difficulty working out my download.php script. The customer gets a unique download link generated from my database and when they click it on it is meant to send them the file from my server. Only in my case the zip file is always corrupt and bigger then the original file. Original file is 68KB and the downloaded file ends up being 90KB.
Here is my code that sends the file to the browser:
<?php
$actual_link = "http://$_SERVER[HTTP_HOST]";
$post_id = $wpdb->get_results("SELECT transaction_id FROM slx_jomsocial_plugin_orders WHERE (transaction_id ='". $tx ."' and unique_code='". $token ."')");
$rowCount = $wpdb->num_rows;
if($rowCount==1){
$name="Unzip_First_Video_Embedding.zip";
$file_url=$actual_link."/jomsplugins/".$name;
header("Content-type: application/x-file-to-save");
header("Content-Disposition: attachment; filename=".$name);
readfile($file_url);
echo "<h1>Thank you ".$name=$_SESSION['s_name']." For downloading the plugins.</h1><br />";
}else{
echo "<h1>You are not permitted to downlaod, Please purchase plugin first.</h1> <br /><div style=\"margin-left: 25%;margin-top: 1%;\">Click Here</div>";
}
?>
What am I doing wrong here?
UPDATE:
I have been experimenting with the script but still my files come out corrupted (Unzipping them gives a .cpgz file). Here is my current script now:
<?php
$actual_link = "http://$_SERVER[HTTP_HOST]";
$post_id = $wpdb->get_results("SELECT transaction_id FROM slx_jomsocial_plugin_orders WHERE (transaction_id ='". $tx ."' and unique_code='". $token ."')");
$rowCount = $wpdb->num_rows;
if($rowCount==1){
// set example variables
$filename = "Unzip_First_Video_Embedding.zip";
$filepath = $actual_link."/jomsplugins/";
// http headers for zip downloads
header("Pragma: public");
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: public");
header("Content-Description: File Transfer");
header("Content-type: application/octet-stream");
header("Content-Disposition: attachment; filename=\"".$filename."\"");
header("Content-Transfer-Encoding: binary");
ob_end_flush();
ob_clean();
flush();
#readfile($filepath.$filename);
ob_clean();
flush();
exit;
}