Let me rephrase. You can't be more than C without ever having driven with somebody else. As you already had A or B, this isn't relevant to you.
But what probably happened is that your first sessions were rated like A or B, and later on you had some less cleaner ones rated C. You seem to be at the very edge between C and B, so just move on and have some good races or clean laps and you're back in the business