University admissions will want you to do well in the high school that you attend. They do not expect you to fix or change your high school. You will not be penalized for not taking classes that do not exist in your school.
One daughter attended a small high school that offered no AP classes at all. She was still 5 for 5 in university admissions (with merit aid from most of them). She did self study and take the AP Spanish class, but her Spanish is very good and she had already spent a semester in a Spanish speaking country taking all of her classes in Spanish. I do not think that this impacted admissions at all.
AP music theory is a tough course, or at least quite a bit tougher than some people expect.
The daughter who took no AP classes went to university and found a classmate that was bragging that the classmate was far better prepared for biology since she had already taken AP biology. This turned out to not be true either. Our daughter was just as well prepared to take university science classes including biology even without taking any AP classes in high school.
I do not think that you have a problem here. I would either not bother self studying and taking any AP exams, or only take very few and only if you want to.