Yeh do go, there's been loads of times I've been petrified in such circumstances - but it always pays off well for me. Like when I thought I couldn't play my music for a musical this summer, I went to the band call, and I played quite well, and the director couldn't stop saying how thrilled he was with the band. Or the first musical group I ever joined - I was forced into my youth orchestra at 11 years old, and didn't play a note for the first 3 years. Then the trom section of 7 all left at once, so I was forced to play, and from there I progressed a heck of alot.
So what I'm trying to say is I'm sure it's a terrifying prospect for you, but it should be enjoyable once you settle in, and you'll make some great friends and probably have a laugh doing something you love. Out of 2 players - the superb player who doesn't care/ is a total snob, and the enthusiastic player who is totally commited to what they're doing - any MD of bands etc I play in would choose the enthusiastic player.
I strongly encourage you to go