Should I ask my teacher for a pass/fail grade if I have a C in the class?

It could definitely help in making your grades in math look better. Instead of being a low grade, it would be a pass instead. If your school uses ranking it won’t necessarily help to boost that, and I’m not sure how moving from a Letter grade system to a pass/fail system would affect GPA.

The chances of the teacher agreeing to change your grading system are probably not good— unless if this is something they do in their class anyway, they likely won’t make any exception for you. That being said, If you can convince your teacher to change, do it! You don’t know until you try.

You could definitely try! A C is going to make it quite difficult to get into Harvard. A 'pass' in a class in which everyone or nearly everyone else received letter grades isn't going to look great, but it does sound better than a C. I think most high school teachers and high schools generally don't allow this, though.

You can't get into Harvard with a C.