It’s not about the amount of A Levels you take, it’s about the grade at the end. Oxbridge would rather A*A*A* than A*AAB. When I applied for Cambridge, there were people on the student room chat who had 5 A Levels predicted all A* who didn’t even get an interview. Doing 3 will not put you at a disadvantage. Just perform well in entry exams and interviews, and you will have a good chance of an offer.