Phlebotomists, I need your input?

All of this is stemmed from me getting a new job at a hospital. I currently work at a one man draw station. I have been a phleb for 2 years now. I worked at a hospital for one year before this draw station. I feel like I am aweful at phlebotomy. I see 20-30 patients a day and I completely miss about 3-4 a week. :( I am much better than I was at the hospital when I was starting out, but I feel like I should be better. Am I crazy? I have a lot of anxiety about my new job which pays double the salary. I am afraid I will get there and they will see that I am not good and then I will get fired. How good should I be at this point in my career? Help? Am I overthinking this?