My 90 day eval for work is tomorrow! Is it normal to make little mistakes?

Okay, my last question was on my work performance. To follow up on this I want to be more specific. I began my job as a college student about to graduate. They really liked me and gave me the chance to start 30 hours a week until I graduate. I graduated a month and a half ago and now I am full time. My position is a new position which the person before me quit by the fourth month. I have always worked with children or in a school setting, this job is mainly administrative and deals with money which makes it more stressful. I feel that I have been doing the big things right, I am caught up with everything. The thing is, I messed up in the addition 2 times due to some complicated receipts, I in turn got a huge calculator with paper roll to help me with it. That is mistake number one. I have not messed up since, I have to admit, the calculator helped. I however, continue to make little mistakes such as forgetting to put down a name on a document (actually, it has only happened once: today). Anyway, there are more times I messed up on the little details that make a huge difference, but I can't remember right now. I am also very shy and not very confident since I am required to learn all of the new things that we have to do as a company to be in compliance. I am stressed I do admit, but I am trying my best. It's the small mistakes that get me. I have been there three months and a week, my 90 day evaluation is tomorrow. I am nervous, I feel like I can improve so much, I am just until this day still trying to catch on to the new rules and regulations. Is this normal? I have no idea how my eval will go tomorrow, but I do not feel it will be good.