Despite all I'm saying on working to make your performance great, this is not a test. This is the reason you got into music. Music is a performing art, so enjoy this and every performance. Yes, a part of your brain is dedicated to monitoring what you're doing, how you sing and play, stay in tune, in time, on target. But an equal part of you is to enjoy getting to sing and play. How wonderful for you - to get to make music and have people listen!.
Warming up is great, but spend regular time trying to get to 100% performance level with no preparation. Be instantly on.