One of my kids had intense commitment to music during high school. This did not affect grades but did affect the rigor of course choices. They still got into a top school (Harvard).
Are you applying to BM programs? (Conservatory or School of Music). Then the audition is the main criteria and academic requirements like GPA may be more lenient anyway, depending. A 3.5 is not a bad GPA.
If applying to BA or BS programs, which generally do not involve auditions for admission, it is helpful to submit a music supplement with a recording/video (can be one piece, cued, but ask the schools; maybe samples of different aesthetics or genres), a music resume (including practice times) and letters of recommendation relating to music. I believe the supplement really helped my kid.
Your guidance counselor can write about your commitment to music inside and outside of school. Schedule a meeting with them to discuss. Much better than you trying to explain, which can, yes, sound whiny. Colleges understand and respect commitment to music. Stand by your choices. The GC should not explain grades but simply say you had substantial, intense commitments outside of the classroom and admissions can take it from there.
Again not clear on where you are applying. You might wander over to the music major forum, which is not only for music majors. Make sure to read the Double Degree Dilemma essay in the Read Me thread on that forum, which is really about ways to continue or study music.