You mention all the time you spent, all the work you did.
You mention extra credit. You don’t mention getting the answers right on the tests.
You were failing at the midterm-- what did you do to increase your grade other than ask for extra credit? Did you attend office hours? Get a tutor? Put in extra time on the reading? Do any outside research?
Your grades are your responsibility, not his. You speak of what he did. You had a D at the midterm. How did HE ruin your grade??
What did you do?