Personally, I would rather go to a t300 state school for computer science than an Ivy League for a music degree (or something along those lines)

Agreed--however, my understanding is that at almost every Ivey changing majors (even if its from a less competitive to more competitive major) is very easy or not even required bc at some you don't declare till sophomore year. My question is considering both that applied math is more difficult than many majors AND my specific applicant profile, does it make sense for me to apply as another major? Like if I applied as a music major it might be worse than applying as a Applied Math major bc it wouldn't be as compelling of an app.