Because of stage fright you can easily lose focus and control over your performance. Your breathing becomes shallow and not stable, your body starts to shake and your overall feeling is quite hopeless.
All you want is just to get over and finish the piece. But even then you can make mistakes at places where normally things go pretty smoothly. You might even make a complete stop and start over or start crying and can't continue playing. After such performance you swear not to play in public ever again.
Whatever the case might be stage fright or performance anxiety is a perfectly normal feeling. With time and experience you will learn to control it, you just need to play a lot of times in public.
Playing the same program more than once is a great idea. By performing the same pieces over and over again in public you will start to feel that confidence. Also there is one thing which can save your day - it's breathing.
If you feel a lot of stress and stage fright, try to become conscious of your slow and deep breathing through the nose. This technique will help your mind stay focused before and throughout the performance.
In addition to breathing, try to focus on the current measure you are playing. Nothing else matters - just you and this measure. Then the next measure and the next.
But you have to really force yourself to do it. Not to focus on any ideas or thoughts which come during the performance. Instead, let them go and steadily pay attention to the current measure and your breathing.
Don't beat yourself up if you make a mistake or two. Again, let it go and keep up your focus. Make your breathing regular and rhythmical. Exhale and inhale within pre-determined number of beats in your piece. The mind is like a muscle. With time it can be trained.
The feeling should be that your body is relaxed but your mind is on fire. Then you will not have any stage fright.
By the way, do you want to learn my special powerful techniques which help me to master any piece of organ music up to 10 times faster? If so, download my video Organ Practice Guide.