That's a nonsense distinction. I was going to write 'over my skirt' but knowing the clunky English DL often prefers, went for 'on top of'. Both should be accepted as correct.
It can mean both on/over and about, and the same applies in English. "A cat walks on (top of) (= over) my desk." "The lecture was on (about) the pandemic." The same word has the same two senses in Spanish as well.