Look man, you're going as FRIENDS. Don't dump the one you asked. You sound like a decent guy, and I'm sure it would get to you later. You wouldn't be that popular any more either if it got out that you bailed on someone at the last minute and took someone else. It's good that you asked someone from your class. Lot's of senior girls don't have dates because senior guys are going out with juniors and sophmores. HS was the most fun years of my life, but I don't envy you guys nowdays. You got more STD's floating around than the Spanish Armada had ships. People get mad at you now, they don't threaten to beat you up, they threaten to shoot you. Anyway, just stick with the girl you asked. You'll be glad you did. Save dating the "hot chick" for when she breaks up with her boyfriend.