It would be worth looking at other more viable career paths in music/the arts. Being a professional musician isn’t the end all be all of a music career; music education is certainly something you could look at, and it’s very possible to be a successful music educator and live well.
However, it is also very common for many new college students be undecided. Don’t worry, you will meet plenty of people who are in the same boat as you, and there will be advisors to specifically guide undecided majors. You’ll probably be taking some gen-eds at first anyways, and you certainly have 1-2 years to settle on something.
Being homesick is completely normal too; maybe it will seem to you that everyone around you is assured and settled in right away, but I promise you that almost everyone will be homesick to some degree. That being said, you should definitely make the effort to make friends. Join clubs that sound interesting, keep your dorm door open, talk with your roommate, try to find at least one person in your class to work with. Also, in the first weeks, most people in your dorm will likely eat together, so join them or take the initiative to invite some people to dinner. I’m an introvert as well, and I know it can be really exhausting and scary to put yourself out there with near strangers, but this is something you’ll need to learn to do.
I have no idea about how lively Swarthmore’s party life is, which can play a factor in how easy it is to find friends who don’t party or find activities that don’t revolve around partying. From my personal experience at my college, I was to able to find friends who virtually didn’t party and we had a lot of fun doing other non-party/alcohol related activities.
Bottom line is- it’s completely ok to feel apprehensive about college. You are not alone. Try to keep an open mind and try new things. Good luck with the waitlist and Swarthmore!