Low grade on edX Course

So, I reported on the app that I am self-studying AP CS A, but didn’t specify the source from which I am studying. I took 3 out of the 4 courses in edX, and scored good grades on all except for the second, in which I scored 76%. This happened because, during the final week of the online courses, I had the SAT on 4th of December, and the deadline was 5th, and I mixed the timezone of the deadline, which resulted in me missing the submission dates for the final week of the course (including the final exam).

Should I, in a bullet point, explain this in the FUN updates form, should I just leave it there (given the other 2 good marks, AO might consider that there were special circumstances), should I skip mentioning the mark in the grades section (I’d rather not do that, since that will be somehow trickery), or what would the best course of action be?

My suggestion, email MIT admissions!