In the confirm page you sent, you aren't using that code, the confirm page you sent is using this instead:
$mhqFee = WA_PP_ECO_GetValue($WA_PP_ECO_DoResult, "FeeAmount");
$mhqGross = WA_PP_ECO_GetValue($WA_PP_ECO_DoResult, "GrossAmount");
$mhqDonation = $mhqGross - $mhqFee;
I'm confused. the code you say you are using and the code in your pages is not matching, making it very difficult to tell what you are doing wrong.