First I want to clarify something that was mentioned by another person here. Graphic Design is NOT the same thing as 3D animation, they're two completely different disciplines with almost zero overlap.
That being said, graphic design and web design have a lot in common and in fact the end product ends up being much the same, it's the delivery method that's different. Many graphic designers actually end up going into web design after learning some coding and polishing up their portfolios. So if you end up going into web design, you'll actually end up taking many of the same classes that a graphic designer would take: typography, design, color theory plus classes where you could put all the theory into practice, i.e. graphic design 1, graphic design 2, etc. These will basically be your portfolio building classes. You'll also need to learn certain software programs that are commonly used, such as Photoshop, Illustrator and Indesign,
As a web designer, you'll need to have all the design principles down, and in addition to Photoshop and Illustrator you'll need to have a handle on the scripting languages that make the web run: XHTML (HTML is slowly being phased out), CSS and Javascript for starters.
If you do go into web design, you'd do well to hang on to your advanced math skills. I know, I know, it sounds counter-intuitive (art and math?) but this is why: Web design and web development have quite a bit of overlap. Web development, unlike web design, is the actual coding and handling of the data of the web. This website (Yahoo answers) would not run were it not for some web DEVELOPER working under the hood and leaving the "making it pretty" to a web designer. What does this have to do with you? Well, if you do any job searches for web designers, you'll invariably run into companies looking for somebody with HTML, CSS, Javascript experience that can also do some programming. You'll make yourself more hireable if you can do both aspects, and that would mean learning PHP, Java, XML, maybe PERL and some CGI. These are heavier duty than HTML, harder to learn, and in the case of Java, a full-blown programming language. In order to get the most out of these, you will need to hang on to your math skills.
So here's my suggestion to you: Take a look at graphic design and web design. In college your foundation classes will be the same for both which will give you plenty of time to make up your mind. If you decide to zero in on web design, take some web development courses as well.
For right now, do take some art classes in high school as most art schools will require a portfolio review before being accepted.
As far as what art colleges to go to? There are many, many, many. Some of the better ones include Ringling, SCAD, Academy of Art University, CalArts, RISD, Pratt, etc. Take a look at your local colleges as well, many state schools have excellent art and design programs. Avoid the private chain schools.