I continue to make little mistakes on the job and I have only been there for 3 months...?

Tomorrow is my evaluation, honestly, I feel like I have not been doing well. My job is stressful, I am in charge of scholarships. I keep making small mistakes such for paperwork and the girl working payroll is over stressed and gets super mad. I am also very shy, I am not sure what will happen tomorrow. I need advice. Is it normal? Shouldn't of I have already caught on by the end of my 3 months?