Mysql insert query runs many time on download after form submit - php

Question

Mysql run more than once while i try to download with download manager.
if(isset($_POST["fname"]) && isset($_SESSION['token']) && $_POST["token"] == $_SESSION['token']){
// after submit it runs two times
$sql = "INSERT INTO testpage SET
username = 'test',
name = 'xyz'
";
if(!mysqli_query($db_conx, $sql)){
echo mysqli_error($db_conx);
exit;
}
$fullPath = 'user/pdf/xyz.pdf';//let the path is this
$basefile_name = "abcd" ;
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename=' . basename($basefile_name.".pdf"));
header('Content-Transfer-Encoding: binary');
header("Cache-Control: no-cache, no-store, must-revalidate"); // HTTP 1.1.
header("Pragma: no-cache");
header('Expires: 0');
header('Content-Length: ' . filesize($fullPath));
ob_clean();
flush();
readfile($fullPath);
exit;
}
if (function_exists('mcrypt_create_iv')) {
$token = bin2hex(mcrypt_create_iv(32, MCRYPT_DEV_URANDOM));
} else {
$token = bin2hex(openssl_random_pseudo_bytes(32));
}
$_SESSION['token'] = $token;
and the html part is
<div class="container">
<form method="post">
First name: <input type="text" name="fname"><br><br>
Last name: <input type="text" name="lname"><br>
<input type="hidden" name="token" value="<?php echo $token; ?>">
<input type="submit" value="Submit">
</form>
</div>
Still have problen even after adding token where i am wrong .
thanx in advance . php mysql.