Hi Graded. Try playing more around people. I know it may be hard at first. Go to music stores and try out some pianos. You can go to senior centers and play for seniors. They usually love it even if you stink. Go to Hotels where they have pianos hanging around and sit and play. the worst can happen is they ask you to stop. Play in front of people alot. Record yourself ofen. All of this helps. Invite friends over and tinkle the piano in front of them. Practice in your mind thinking of the audience you will play for , and then blocking them out and thinking only of your music.
Other things, - when you walk out onto the stage, walk confidentaly. Walk like it is the audiences pleasure to hear you. do not and I mean this walk out like a dear in headlights.
Just like you practice your instrument - practice your stage presents. Go thru it in your mind. Try it out in advance if you can. You walk out and smile and acknowledge the Audience. You note where the piano bench is. Go thru it all. If you have a friend have them video tape you as you approach the Piano.
Hope all this helps.
Cheers, Becky