To add my own two cents:
Do run-throughs of your program in front of anyone and everyone, on different pianos, and at different venues and times. Playing in front of others is like working out at the gym; it really does build a kind of a strength, although unlike weightlifting, the strength is internal. Also like exercise, you need to keep it up in order to continuing reaping the rewards of your efforts. Performing once a year is comparable to exercising once a year. If possible, try to perform for people several times per week. Invite your neighbors, friends, family, strangers, in short anyone who will listen, and play for them as often as you can. Before long you'll be a first-rate performing athlete. How you play is another topic, but your nerves should be under control.
Many of us on this thread have brought up bananas. Keep in mind the active ingredient of bananas is Potassium. That is what relaxes us. I don't do this any more because I don't feel the need, but it was very helpful to me when I got terribly nervous to buy some salt substitute, which is Potassium chloride and dissolve about a half a teaspoon in some water. That was a larger dosage of potassium than in bananas, and calmed me down even more. It really does work to calm nerves without impairing motor dexterity. I just wouldn't take more than half a teaspoon, which is already two servings.
Another approach which has also helped me a great deal is visualizing. For several days before your recital, visualize yourself playing your pieces in front of the audience for about 5 minutes at a time (or longer if you wish). Imagine it going well. When it comes time to cross the stage and play, you'll feel much more ready for it than you otherwise would.
Lastly, if you find yourself preoccupied by nervousness, take that as a cue to concentrate more on your music and piano playing. Whenever your mind wonders towards your nervousness and fear, just resume concentrating on your piano playing. Meditation can help with that as well.
Good luck dealing with this common problem!
Steven P. Niles
DMA, Piano Performance, USC Thornton School of Music
Instructor of Music, Los Angeles Mission College
Instructor of Class Piano, Rio Hondo Community College