There's lots you can do for anxiety! There are some very good anti-anxiety medications out , and they really work.
I had a couple of public speaking engagements in the past few months and what helped me the most was, right before going out there I would say out loud to whoever is there with me, "I'm going to have a great time out there, it's going to be really fun". For piano performance I guess you could say to yourself, out loud, "I just love those piano pieces I've learned, I'm going to have a great time playing them. Once I play the first note, the hardest part is over it's all fun from there!"
Also, I think about how the audience is really rooting for me out there. They are there because they have fun listening to piano performances, and they are there to simply enjoy themselves, no one is there to be a critical jerk. What's the worst thing an audience can do, realistically? They're likely chided themselves in their head if their mind is wandering and they're thinking about their to-do list, or what their boss said.
One more tip, make sure you have a healthy meal before you go on stage so you're not hungry, and have a good, restful night before the event too. Finally, reward yourself immediately afterwards, like going out for a nice dinner, or getting yourself a little gift. Then, focus on how much fun you had playing at the performance and how good you feel, try not to dwell on the nerves.
Topic: please help me!!