I feel very much the same way and I have avoided subjects that I've liked for the same reasons. School at higher levels can be so critical that it can induce a kind of learned helplessness... There isn't enough reward and there is a lot of punishment and negative feedback. Some of my hobbies were ruined because of school burn out. I haven't really been able to fix it. One course in particular I took purposely failed everyone on every assignment to prove a point, then they did some mathmagics on the marks at the end so at least some people would pass. It all felt very hostile and I had no way of really knowing the true quality of my work, even when I pressed the TAs to explain the marks they were vague and distant. I went from loving essays to hating them and not caring about school because of that. It felt like there was nothing I could do to improve, I was just a punching bag for disgruntled TAs.

What people are saying above is true, but it's easier said than done. I've always been made to care about grades and it's hard to let go of that when your entire life it's been the goal. If you can somehow switch how you feel rewarded from external (grades) to internal (judging the quality of your own work) it would make things easier I think. I haven't figured out how to do that for myself. I feel like I've been hard wired to accept what authority figures say as truth, even if I consciously know they're full of it.

From people I know who have graduated though, the grades don't mean anything compared to an excellent portfolio, resume, and networking. If what you want out of this is a paid career then don't worry about getting the top marks, worry about adding value to yourself and retaining your passion so that people will want you as a musician, music teacher, composer... or whatever it is you aspire to be.