I can certainly understand your getting nervous because there are a number of things that can go wrong in a live performance. The good news is that the more you perform in front of people, the easier it gets. With experience comes confidence and it is that confidence that makes playing live much easier. I would suggest that you play for people every chance you get, whether it be for parents, brothers and sisters or friends. It is extremely important to be thoroughly prepared. You should have worked through all of the problem areas of your piece(s) and if any problems do still exist, you should know exactly how to overcome them. For instance, if you reach a passage that you think you might forget, is there a place earlier in the piece that you can immediately go back to without a gap and then give it another shot? This is not ideal, but problems do happen and it’s important to know how to keep moving forward. Remember, many people in the audience might not detect the mistake if you can continue seamlessly.
I have found that slow, deep breathing helps to calm down when necessary before a performance. Do this for about 10 minutes before you go out on stage. When you get to the piano, take your time. When we’re nervous, time seems to go by much more quickly and we hurry without realizing it. Take time to adjust the bench, both the height and the distance from the piano. The audience won’t mind waiting and it only takes a moment. Most mistakes happen right at the beginning of a piece because students tend to begin playing before they are completely prepared. Get your hands ready and count to three before starting, this will ensure a strong beginning. Finally, become very familiar with the final cadence and if disaster does strike and you feel that you cannot recover, go directly to the end. Again, not ideal, but it’s a way of finishing the piece rather than stuttering in the middle.