I don't know how much advice I can give. Mostly because I'm the same way.
I'm in band, and get so SO nervous about anything. I get nervous about TUNING, my flute!! It's crazy. But it's also like, almost uncontrollable. For me, at least. But I'm trying to become more self-confident.
And obviously, I've learned, the only way to do that is by "facing your fears" you have to find your limits and push yourself beyond. Go outside the box. Don't go too far, or you'll scare yourself. But you HAVE to expand otherwise you'll always be cooped up inside that little box and who knows what awaits you out there.
And you HAVE to try new things, because you never know. I tried soccer, softball, dance, and then I joined band. And although I quit the first 3......I love band. It is my LIFE. And I can't even tell you where'd I'd be if I had been too nervous to try it.
Or marching this year!! That was a big choice, and I knew it'd be hard and scary and it was. But omigosh I don't regret it at ALL. It's helped me grow in music, as a person, I made a bunch of new friends.....it was SOOOO much fun I can't even put it into words.
So. I guess I would tell you too go for it. Because you never know. And I know that, if you hated it, you would be strong enough to get through it.....and then you'll KNOW and you won't ever have to do it again. But you'll know you tried, and thats all that matters. And you don't know.....you could end up LOVING it.
I think, if you can, try out for a small part. There are always small parts that'll get you on stage.....but not TOO much.
Thats not very good advice, but it's all I've got. I hope it helps a little.
I hope you tryout and if you do.....GOOD LUCK!!