look for these lines of code in your confirm page
$nextIndex = count($AuthNet_optional[0]);
$AuthNet_optional[0][$nextIndex] = "x_email_customer";
$AuthNet_optional[1][$nextIndex] = "TRUE";
and set it to FALSE like so
$nextIndex = count($AuthNet_optional[0]);
$AuthNet_optional[0][$nextIndex] = "x_email_customer";
$AuthNet_optional[1][$nextIndex] = "FALSE";