Thanks everybody for your comments, I just remembered that I didn't leave any response here after all of your advice.

By the way, heero_yuy2, please don't imply that I don't know how to take responsibility. I wasn't looking for excuses to lie or hide from this guy. I was asking for help on the right way to explain things, since I didn't want him to feel like I was being snotty or whatever.

To the rest of you, well. I'm not as young as you think, haha, let's just say prom is long gone. But perhaps I seem a bit childish because I haven't experienced this sort of thing before...in my family (yep I'm Muslim) dating is definitely not the norm so I didn't immediately catch on to the idea that the guy was "asking me out". I never even realized that he liked me in that way. Yeah I'm slow.
Anyway. I took into account a few *sane* suggestions here and the problem is sorted out now.

Thanks again to all. :)