I don't know if I have anything to say to make you feel better, but here is my experience. I had these fears early on, but they seem to have abated (I've found other things to obsess about). What I kept reminding myself was, even if something happens, at least now I know I can get pregnant, and if something does happen, I will be able to try again.
It also helped me to remind myself that nothing I could do would cause a miscarriage, and if I did have one, it was because there was something wrong and it wasn't meant to be, and I would be able to try again.
A woman on one of my other boards (preg with her 4th) would tell us to tell ourselves, "No matter what happens, I am pregnant today."