This!
Wanting them to know how “strenuous” your piano activities were, will only point out that you couldn’t handle the strain.
My children are/were all violinists, with various awards at state levels. Dad is/was a violinist and began their training at the age of three. They also were state-ranked tennis players. The funny thing is, they really liked practicing! They even brought their violins to the tennis courts! (practice playing while waiting for their matches!) We didn’t have to drag them anywhere.
Their “focus”, in their applications, was on their academics, and what they hoped to study, achieve, and bring to their Universities.
I know that the guidance counselors, at their high school, explained to all of their students, that the universities really wanted to see how all of these experiences would contribute to their universities.
If your piano experiences were really that strenuous, then it’ll look like you didn’t enjoy what you were doing and That the activity was not intrinsic but extrinsic. They don’t need students who will make excuses for their grades. Your grades are your grades. And the 3.5 is not bad.
Edited to add; they all had 4.0’s. They all were national merit finalists. Plus, they got into top 10-20 schools. Each of my children chose and attended their universities, based on how they felt about the “personality” of the University.