Don’t dispute it. If you wish to ask if there is something extra that you can do in order to earn that last point, I think it’d be viewed more positively than whining/complaining/criticizing/begging. It’s constructive and demonstrates that YOU are the one willing to do something to get a B… But you need to be able to walk away if he leaves it a C. There are many, many things in life in which there is a cut-off, and in this case, close as you came, you missed it. I know if seems lousy – it would have been easier to have missed it by more – but so it goes.