There are two links on the page that the Buy Now button takes you to. One is a link at the top that says, "Buy now to experience the full game!" Don't click that one. The other one is a link at the bottom (next to the price) that says, "BUY FULL VERSION" and that one will take you to the correct purchase page. Just check to make sure that the correct game is listed at the top of the purchase page and you'll be OK.