Every audience is different, and some nights, no matter how hard you try, you just can't please them. I remember one production I did, everyone always nearly peed their pants when I gave my monologue. But I always held just a little bit back. Finally, closing night, I gave it my all, and I swear - you could hear a fly snoring if there was one in the house.
What's important is that you give the best performance you can. The audience will love you (unless they're supposed to hate you and then, they'll LOVE hating you) and you'll have a ton of fun. And you'll be GREAT! :D
Break a leg!