If you're receiving 2 emails instead of one - probably you need to remove that second mail() function call that was added previously.
As for adjusting From: field in the email confirmation to user, you need to set headers parameter (similar to how this is done in your code above for email notification to admin. Here is the complete code:
$my_email = 'me@xxxxx.com';
$mailheaders2 = "Content-Type: text/plain; charset=us-ascii\nFrom: Website Name <$my_email>\nReply-To: <$my_email>\nReturn-Path: <$my_email>\nX-Mailer: PHP";
if ($send != "false") {
mail($to, $subject, $msg, $mailheaders); // mail sent to admin
mail($_POST['Email'], $subject, 'Thanks we received your info',$mailheaders2); // confirmation email
header("Location: $relocate");
}