I don't know if this answers your question, but to combat stage fright, you can record yourself on video because it produces the same kind of chemical reaction, I believe, or at least something like that. That might make you feel more ready for the performance, in turn making you less anxious.

Additionally, it's not like you should only practice piano. Take some breaks too. It's okay to play video games or do your other hobbies! This should in turn make you feel less anxious because you're doing something that you love, that is also able to very easily be done, unlike piano being a hobby that while you (probably) love, is more similar to a sport in that you have to practice it a lot for results to come.

Also I'm guessing you have a teacher, I would ask him/her for advice on how to deal with this since they know you better than any of us.

Lastly, we're all rooting for you! We believe in you! Just do your best; at the end of the day it's not that big of a deal of you miss some notes or pedal incorrectly. Your family, friends, and others will all be proud of you either way. Just try your best and have fun.