It can be daunting going into anything with the idea you're going to fail. And sometimes we think the best way to avoid that failure is to not even try at all. But if you don't allow yourself to try new things, and do things even if you think you're not ready, you won't reach desired destinations and basically stay in the same place.

So go to rehearsal, go to the audition, simply show up and you will be much better off than not going. Even if the outcome doesn't end how you thought it would. You will still gain experience from going that you can use for future situations.

Another layer of this is showing up mentally. If you physically show up to rehearsal, but have a negative attitude you won't get very far and will probably drag down the people around you. If your attitude is sad, upset, pouting, with a "pity me" mentality, you will have a rehearsal that reflects that way of thinking. But if you show up with a positive, excited, and "let's do this" attitude you will see more positive results and that will also have a positive effect for the people around you.

So show up on time with a fully engaged mindset, ready to learn from every mistake you make, and you will see much more progress than not showing up at all.