Here's the problem:
[php]
$to ="you@yourdomain.com";
[/php]

Change to (and change the you@yourdomain.com appropriately)
[php]
$to ='you@yourdomain.com';
[/php]

and I will add that the script is unecessarily resource intensive; hard to follow due to improper indentation and using " where ' would have been preferable; doesn't teach how variables and strings ARE different (you don't need to and shouldn't put a variable inside a string on it own); uses outdated and depreciated HTML standards (without even a <!DOCTYPE>); and doesn't use TRUE and FALSE definitions ( $send = "no"!? What kind of rubbish is that? )