Call and ask them to honor the price. If the reservations folks won't do it, try web services. But I've always had good luck with the reservations desk.

There are also some other suggestions here (you'll have to search unless someone else wants to find it) about clearing the browser cache, etc., trying to get the original price.

ETA: I've always called before the end of the hold period. If you've waited and the hold expired Friday night, you're probably out of luck on that reservation.