I'm a brand new nurse, too, and always dreading the fact that one mistake is going to end me. But I'm starting to change my mindset. You can't always be thinking about it that way. Focus on all the good things you're doing, the little things that make you proud... like, "Yes!! I drew blood on my very first attempt!" or "I knew my patient is in isolation and I made sure to get everything done at once in the patient's room!" or "I called the doctor and explained to him what happened!" It really is the small things that keep me going and keep my head up. And if something bad does happen, well, it was meant to be. Whatever happens happens. We all have our own path in life. In the end, we will be where we are supposed to be.
I COMPLETELY understand as I, and many others, am in the same boat. Don't ruin your days off by thinking about work. Leave work at work. Enjoy your time away. Wherever your head is is where your body is.