Mid-year report: should I explain the C

I have one C in an honors class which I tried extremely hard to get to a B but ended at 79.9. My luck. I’ve applied to a few selectives such as UW Madison and a few reaches, and I don’t want to appear to be slacking off. UW Madison provides a text box along the lines of “if you have any comments about you report, write here”.

Would it be a good idea to explain it or would it make me look fake and desperate? It’s a weighted class so it’s the equivalent of a B in regular but I’m sure it would look bad in comparison to other applicants. It’s my only C since freshman year so I’m freaking out.

I’ll message the explanation to anyone who’s interested to help me out with advice.

What would you say about it? Were you extremely ill? Did you have a death in the family? If it’s just I tried really hard and missed the B by 0.1, no.