I checked out your site, since the code is hidden I can't see exactly whats going on but I can try to help.
I believe you merged the confirm and checkout page together there are hidden fields that need to be carried to the paypal standard page. Also on the check out page you have billing and shipping. Unfortunately you don't need both biller and shipping because paypal standard only ships to billers address they don't have a choice there, sorry.
Get rid of one of the forms and I would leave the checkout and confirm pages separate because paypal standard is difficult that way and webassit although capable isn't as fully customizable as you would like so leave it as it is.
Why did you make me go to your Florida Keys Fishing page, I live in Florida and try to go to the Keys whenever I can. Now I have fishing on my mind. If you need more help you can contact me by replying.