I was asked to prom . .?

My friend Tom(he's a senior) just asked me if I'd go to prom with this girl named Terra(senior). The thing is, I'm only in tenth grade, I might have spoken to her once in my life so I know nothing about her AND I know this might be shallow but if I don't know her personally I have nothign else to go on other than looks and . . she's sorta ugly. . I'm generally a nice guy but I always imagined prom as something I'd wait to do for my senior year and with a girlfriend or something . . is it that big of a deal if I say I'm busy or can't? Or should I . . you know, . .go?