People make mistakes all the time. My husband, who is a computer expert, says that intelligent computers make even more mistakes than dumb computers. Maybe it is the same with people.
When you receive a task to do, it is stored in your short-time memory. At that moment it feels like you will not forget it, but it is exactly what happens with everything you have stored in the short-time memory. That is why you must write down everything immediately.
You should either do things immediately or write them down. Once a day, read your notes and plan your work. What things need to be done immediately, what tasks need to be done today, and which ones can wait?
About the numbers: always double-check them or ask a colleague for help with that issue.
We all learn from our mistakes. A mistake is an excellent way of learning things. Every time you make a mistake, you should reflect on how to avoid making it again. Learn to organize your life and tasks to avoid mistakes.
After you are finished with your studies, you will hopefully get an interesting job. Making many mistakes could be a sign that you are not paying attention to your work because you have little interest in it; or maybe a signal revealing that you are tired, even if you need this job for the money. Do you make as many mistakes at the university or in your private life?