Are you worrying about not having enough confidence in your organ playing? That you don't trust yourself in a public performance and experience performance anxiety?
I think confidence comes mostly from experience.
From having sat on hundreds of different organ benches and played in front of an audience.
From having made hundreds of flops and mistakes and felt shame and vulnerability.
However, until this happens, there are things you can do:
Put a smile on your face even if you don't feel like smiling.
Keep focusing on your breathing even if you feel like you have more important things to worry about.
This will give you a clear mind to be on top of things.
At first you will really think you're not worthy of success, that you don't belong on the organ bench, that you are faking it.
Well, fake it until you make it.