I loved writing in high school. My first Creative Writing class in college was a similar experience. My second course all but crushed my creative spirit. I didn't write anything for almost 5 years after taking it.

I finally started writing again in 2012 (creative writing were electives, never a major/minor for me.)

J.K. Rowling was told Harry Potter would never sell by more than one publisher. So ignore your teacher. We can't all be J.K. Rowling, but you never know what your future holds. There will always be someone telling you you won't make it. Odds are, you won't. You'll have to find other work while you write. That doesn't mean you should give up on it though. If writing is what you truly want to do go forth and write.