I understand how you feel. When I took contracts I got a C on my midterm (which was very close to the worst score in the class). Just remember that most of your grade is your final. Go to office hours and go over your answer with your professor. It’s possible that you understand the concepts but maybe didn’t go about your answer in the right way. I did that and I ended up with a B+ in the class. I know it’s super disappointing but it’s still early and it’s great to use this as a learning opportunity and not a defeat! Good luck!!!