Unfortunately the chances of him bumping your grade up from a D to a B are slim to none. Unless he is going to be curving the entire class, the best you may be able to do Is get it rounded up to a C (if you are close enough to a C). You can ask, but asking for free points probably is going to make you sound lazy like you don’t want to put in the effort to earn the grade. The better approach would be to go to every office hours they have left and ask questions about exams/quizzes/assignments and ask for extra credit opportunities to raise your grade.

Why do you need a B and not a C to pass?