If you are going to play the organ in public, you are definitely feeling some risk.
A lot of things can go wrong.
You can mess up the stop changes.
You can hit the wrong notes.
You can panic because of that and won't be able to find your place in the score.
You'll either sink or you'll swim.
Here's the thing: Given that you do all the preparations and all the homework right, mentally you must be ready to sink.
Mentally you must accept failure and understand that it's not the end of the world.
Only then you can hope to swim.
Only then you can do your best work.
So, are you willing to sink?