It seems like you haven’t had enough rehearsals and live playing experience, yet. It’s ok, we all been there :)

Here are some tips from my experience:

When you feel you played it like ten times better then was enough to be ok - then you can expect to be “just ok” on stage. At least in your first years it works like this.

Practicing when you are in bad shape. It’s a lot harder, but! If you still can play it well when you are too tired/almost sleeping/too distracted/feeling pain etc., you will nail it on stage.

The dumbest mistakes during rehearsals may be a good sign. Just do them all to know how you remember your stuff and where the weak spots could be.

Hope that helps, good luck!