Other than listing the score, my suggestion is to say nothing further about it in the application. There is nothing that can be said that will be viewed in a positive light in these circumstances IMO; the OP simpky needs to avoid casting it in a negative light. And given the disproportionate percentage of 5’s on this exam, admittedly from a very self-selecting group, this is not a feat to highlight.
Now if the high school didn’t offer calculus, my answer would be slightly different.