I wouldn't worry too much about it! If the average was C+, then you were right on average... You can't measure yourself and your future prospects by what grade you get on a three hour 100% final exam. There are so many factors which play into how you write exams that are beyond knowledge, understanding and overall comprehension of course materials. I too took family law last semester (100% final, with a similar class average- perhaps same school) and was frustrated by my grade. However, I realize that future employers also care about ECs, other class grades, experience, and also personality/other more personal things. As a favourite prof of mine always says, C get degrees... and jobs too!