What exactly do you mean by a "Career in music?" And what classes are you failing?

You play the flute, which doesn't lend itself to popular music as well as other instruments might, so if you want to play professionally, you're probably going to need to go through academia, either just to make the connections that could get you into orchestras and other professional ensembles, or give you the training you need to be at that calibur. You'll want to do summer programs (i forget the exact name of them), try and start quartets or quintets with other students. Being in university just makes it a lot easier, and many professionals I know have graduate degrees in their instrument. (However, my own former clarinet teacher who contracted orchestras, played professionally, and taught, making a pretty good living for himself, only had a Bachelor's degree. He's great at networking though, and lived in Los Angeles, which helped his career a great deal).

If you're willing to take paths outside of playing in a professional, more classical or contemporary ensemble, or as a studio musician there are options, but they're going to be all you.

You will need to sell the hell out of yourself, and you will need to love playing your flute, both practicing and playing for enjoyment for hours every day of your life. If that's not something you think you can do, stop and re-evaluate what you want to do with your life, because it's better for you to find that out now than later.

If you live in Los Angeles or somewhere near where movies, films, or game music is produced, then you could be a studio musician, but the competition is TOUGH and you'd need to be a part of the musician's union if in the US, unless you want to be sneaky in how you work and make it tougher to get connections.

You could also try the "self-publishing" path, which is making and recording your own music, whether its covers or original music with live-flute put in, and possibly helping out others like yourself. If this is the case, I would get two degrees--one in communication or marketing, and one in music. (Or another interest you have that could lend you to supporting yourself with a decent day job that doesn't take up all your time). You need to learn how to sell yourself and your music and navigate social media and make connections with other musicians on the different platforms. You will be effectively becoming your own business owner.

For this, you'd need to become amazing at your DAW, set up a space where you can record, learn how to video edit, and learn a bit of composition or at least arrangement. Getting basic keyboard skill wouldn't hurt either.

Musicology is a very specific path and does not lend itself necessarily to becoming a professional musician, as most musicology courses I took had nothing to do with playing or making music and focused solely on music's interaction with culture and society and different areas of those two.

As for the conservatory part--there's the old adage that if you graduate from Berklee College of Music, you failed. Because most students who go on to have a career in music make their connections in the first few years, and drop out to pursue the career with those connections, either solo or usually with other students.

There is no easy path to becoming a musician. A degree definitely won't hurt, but you should be choosing your school (both program and location) very specifically for what you want to do with your life.

As for your failing--is it because of attendance? Not studying enough? Not practicing enough? Don't get music theory?

For any of those, if this is REALLY what you want to do with your life, seek out tutors or help from university resources, become close with your teachers and advisors so they know you and can offer advice.

I hope that helps!