Mike, practice some grounding techniques along with your songs. It's a thousand times easier to stay calm onstage if you've already practiced some ways to be in control of your breathing, posture and nervousness. What works well for me is to remember to breathe deeply, take my time starting, and "grow roots" through the stage and deep into the ground. That keeps me standing straight and not leaning on one leg, and keeps me centered.
It also helps if you start with something you know so well you could sing it in your sleep. First song is not the time for your master showpiece; save it for third if you can, because by then you will be relaxed and able to do it justice.