You're going to prove it wasn't a fluke that you had two great VBACs. You're going to prove you can do it, and do it well.

Give yourself a little bit of time to process things yet. I don't think there's any magic word that will instantly take away your feelings of fear/'stress. I know it's definitely been a process in my case. Every time you start feeling stressed about the upcoming birth, try to redirect your thoughts to the better delivery, and to the things you KNOW to be true about birth. Or just try to tell yourself you can do it and it will be OK. Gradually, I believe you'll start feeling much more positive about the birth.