Dream come true?

I got asked to join a band yesterday... While I've always dreamed of being a singer, i have terrible stage fright. It's my uncles band... He plays drums, and i think there are two other people, but they don't have enough singers, so my aunt asked if me and my sister would want to sing. I know the whole "face your fears" thing, but when i sing, and am scared, my voice gets squeaky and high pitched. I'm fine singing in choir, because there are other people singing with me. But otherwise, I'm not. When i auditioned for my sophomore year of choir, i couldn't even sing the song i prepared because i kept screwing it up so badly, so i ended up singing happy birthday and even screwing that up. it was bad. I don't want to pass up an opportunity like this though. How often do you get asked to join a band, even if it's made up of old Mormon dudes?