The thing that might help the most is the thing that is most difficult to do. Relax. Everyone knows the experience of having you voice "squeak" or break when you are tense or nervous. The more nervous you are, the more your vocal chords tense up (that's my guess, anyway.) In recent years, I've found that the single thing that has released my voice and given it full body is to try to be completely relaxed. In your situation, that sounds like a tall order.
If any of the other suggestions help you to relax and feel more confident, then your voice will benefit.

When I'm nervous singing in a new environment, the first thing I check in the room.. even before the sound system is where the Exit is.

Ya never know..

You'll do fine. People are far less judgmental of us than we are of ourselves..

Jerry