Is the fact that a 100 people are looking at you should be an obstacle for you to play to the best of your capacity?
And what's the big deal that you don't get a second chance? So what? Play perfectly the first time.
When we cross the street, we only get one chance to do it right. We can't say to the driver, "Wait, go back, let's do it again. This time you won't hit me because I will be more careful."
We cross the street safely the first time (usually).
Fear of failure has a big role in making you under-perform in an organ recital or a church service.
But you know what's the antidote to this fear is?
Laser sharp focus.