School Talent Show? Don't know what to do?

There is a school talent show next month and i really want to do it but i'm too scared. You have to peform in front of 800 people but the grand prize is �1000 ($1650) and i could really do with some extra cash as im broke. If i decide to do it i will be singing bruno mars grenade with my mate and my other mate will either be playing the backing beat on the guitar or the keybourd. I am in grade 7 or 6 but i dont get the american grade system. Please help because i dont know whether to do it and i dont want to make a fool of myself. By the way i think i am a good singer and lots of people say i am. Plzz help, no nasty answers.