I sent a "good fit" letter before I got an II, but it really wasn't about why I am a good fit for the school. It was more about why I can handle med school based on the things I have accomplished.
For example, during my undergrad, I have taken 21, 25, 27 credit semesters and even 21 credits during the summer. I said that because I was able to do so while not letting my grades slip, that I feel I understand what is required of me in med school.
Tailor your letter in such a way, because in one of the questions for the secondaries, you already say why you think CCOM should choose you.
Hopefully this helps!