Been there, felt that. Alcohol in small quantities helped me, but too much will make you fall off the stage (did that, too.)

Nervousness affected my fingers more that my voice, but that goes away about the third song.

I love hecklers, because I have plenty of put-downs saved up. The trick is to use them on an ascending scale, mild to vicious.

Have a couple of monologues ready, in case you break a string or something. If you do, ask if anyone can change it for you while you keep working.

Have a good time.