Confidence comes from experience so keep doing what you're doing only with more focus.
Keep trying out as many different organs as you can.
Keep learning as much new music as you can.
Keep performing as many recitals as you can.
That's how you will develop the sense of what works and what doesn't.
But... we will never be 100% confident to take the risk without any fear.
We take the risk BECAUSE of fear. Because this fear demonstrates it's worth it.
The feeling of fear is our compass.
[Thanks to Mae]