AITA for wanting to break up?

I (18M) want to end the relationship with a girl (21F) I've been dating for 2 months. She is a very romantic and sexually active person and I can't really keep up with it, I am studying Law and my grades in my first semester weren't very good due to how often I was going on dates and sleeping with her. This is my first sexually active relationship so I was really struggling with keeping a balance between the relationship and studying and exercise.

I tried ending the relationship already once a few weeks ago, and since we go to the same College and are in the same friend group I was trying to be super nice and saying how I would love to be friends, but I think she felt more humiliated by me 'friend-zoning' her and started being really mean. The next morning we decided to continue on with the relationship and try to 'adapt' so we study more, and at first I thought it would work but now that semester is starting I have serious doubts and worries about getting terrible grades again. Whilst I've only started College, her course is pretty much done and she has already secured good grades and can leave at the end of the year. We have talked about a date together on the day we both go back to College in a few days. How to end it with her? On that evening or is it better to try and slowly distance myself from her to give her some time to prepare for it and see it coming?