Am I wrong for asking my girlfriend to refrain from talking about our exams for just three days?
Why do you want it avoided for 3 days?
I need time to prepare myself.
Taking time to prepare yourself for the exam can be a very good thing. Avoiding the topic with your girlfriend may be unneeded, maybe you can study together.
It's not a learning experience, if I have to study with her.
Being prepared for a school exam is wise. You should do what is necessary to ensure that you are ready to take the exam.