[Squeernemergo]

If you haven't already, gather your grades/tests/papers together and make your case to the professor why you should receive a higher final grade. Talk about things like effort shown in preparation for your 10 minutes a week, and your punctuality to the appointments. Be respectful, as you are trying to persuade somebody to see it your way.

If he insists on the grade, ask him what you could have done to improve that grade. What he tells you is important, so write it down.

If it is a problem to you, and apparently you don't mind burning bridges, you can escalate the situation. But that bridge will be a burning heap from that point on.