Re: ok i feel stupid so please be nice
It is not stupid to be shy.
And I disagree with a previous responder, you do not necessarily fall on your face "a lot of the time." If you do happen to fall on your face, you may get a bruised nose, but bruised noses heal.
Ask the director/coordinator of the band where he/she prefers you to be. With 8 altos and only 2 tenors, I know I would prefer to join in where I don't get lost in the crowd (on tenor). But then, Tenor doesn't get quite as much opportunity to shine. If youre shy, though, it may be an easier place to start.
I encourage you to stay, play a little, and if you're uncomfortable, play just a little more. You don't probably have to stay for the entire session if it's too draining the first time.
You've been invited. Accept the invitation, and see where it leads. You'll do fine.