First take a deep breath. Now just step back and relax. If this is a job where you are expected to just do it, and not think then try your very best to just do it for a while. Then you can really see ways to improve it, and be more productive, and shortly you will be moving on up.
I had this same issue when I became an Office Manager, and had been a hospital RN my whole career. I had to learn billing, and processing payments. These are jobs that took very specific steps, and even though the people that do it only have a short schooling, they understand it. I was very hard on myself with attempts to do it, and things I would get wrong. I'm a bit of a perfectionist, and of course wanted to be able to do it better than anyone. Well that's just stupid. My biller/coder had been doing that specific job for 10 years. You cant learn 10 years of experience in a few days or weeks. There are subtle nuiances that come with every job that are just part of it. Eventually, about 1.5 years in I was good at it. But I can guarantee that if I asked that biller/coder to schedule surgeries, room patients, or do anything other than what she was trained in she would struggle too.
I accepted that it would take time, and I would make some mistakes. Big deal, I would fix em, and life would go on. If you can take that approach, and be easier on yourself, it may be a lot easier to do the job well.