I was actually in the same boat as you. I came to UCF and decided to major in graphic design. After about a semester here, I researched the character animation track and decided to go with that because I love film. I did prerequisites for three years and now I'm in the two year program, half way done.

I have classmates who are following the illustrating and concept art route. When you go through the program, you will be given the opportunity to try all different things while working on your student film with about 10 others: 3D modeling, art direction, production management, rigging, effects, and more. Once you realize what you want to focus in you can become a lead and mainly do that. So you can focus on illustration and concept design, but you will have to take classes on things you don't like. But for all you know you may find a new skill.

I do have friends who have done graphic design. Yeah, you'll have to take classes doing advertising and stuff, but you can take those skills you've learned in your classes and apply them to your own personal work. Whichever major you choose, you'll want to give yourself time to do your personal illustrations.

You can message me if you have more questions!