[Resolvido] Gravar arquivo txt e abrir download

Alguém pode mim ajudar aqui..

meu script grava o arquivo de txt mais da erro na hora do download

teste.php

<?php
echo "<h2>Teste</h2>";
echo '<form name=form01 action="" method="post">';
echo "<p><textarea rows=15 cols=80 name=txt></textarea></p>";
echo '<input type=submit name=action value=Grava>';
echo "</form>";
echo "<hr><br>";

if ($_SERVER['REQUEST_METHOD']=='POST'){
 $nome = uniqid(time()).'.txt';
 $file = fopen("$nome", "a");
 $escrever = fwrite($file, $_POST['txt']);
 fclose($file);

if (file_exists($nome))
{

header('Content-Disposition: attachment; filename='.$nome);
header('Content-Type: '.filetype($nome));
header('Content-Length: '.filesize($nome));
readfile($nome);
 }
}

?>

ERRO:

Warning: Cannot modify header information - headers already sent by (output started at /home/site/public_html/teste.php:2) in /home/site/public_html/teste.php on line 17

Warning: Cannot modify header information - headers already sent by (output started at /home/site/public_html/teste.php:2) in /home/site/public_html/teste.php on line 18

Warning: Cannot modify header information - headers already sent by (output started at /home/site/public_html/teste.php:2) in /home/site/public_html/teste.php on line 19

teste bla bla bla