Treat Art Schools/Programs like any other curriculum. You don't really have a 'choice' on the matter. You go through College for training in your selected field but it doesn't mean that you will do what you like to do while you're at it.
Take for instance my major: Computer Science.
Reason I took it: I love video games. I wanted to be a video game programmer someday.
4 years, not a single time was I asked/told to code video games. I went through the flow learning various theories and programming languages that none of them I am going to use in the real field. I did them anyway because it taught me about discipline more than anything.
I graduated with flying colors, got a job blah blah.
Guess what, I am still not coding video games but that is fine because now that I think of it, I wouldn't want to delve into that field for coding. I actually would rather be a video game concept artist.
TL:DR- Don't let this get you down. Schools prepare you for the path you choose. Learn what you can, expand your horizons even though it's not something that you initially wanted. And you never know that later on you'll discover that you wanted something different after all.
Besides, nothing stops you from drawing manga in your sparetime (you'd probably find a unique personal style too because of the various techniques you learned from school). Just don't show it as school material.
Btw, I never took any art classes but either way, I hope my insights were somewhat helpful













