Tima84
I don't have any magic solution, but I can empathise. I used to suffer horribly with nerves whenever a checkride appeared on the schedule. Even now, 30 plus years down the road from "basic" I still get what I regard as mild stage fright/keyed for check rides/sims.
after a while I got more confident and less nervous
For now, stick with the prep, look round at course mates who have passed rides and think "if they can do it, so can I", and if you do think you've made a mistake, try to put it out of your mind...easier said than done I know.
Good luck, and I hope someone else can come up with something really constructive.