Thank you for your question! It sounds like you are definitely on the right track with the Math, and Physics will be important, too. The current guidelines for an accredited college engineering degree include Chemistry, so taking that in high school is a great idea. As far as picking an engineering track at this point, try the classes that your high school has, and see what you like. Also - not every engineering school puts you into a career box right from the start - places like Harvey Mudd, Dartmouth's Thayer School, Olin College, Smith and others do engineering as a cross-disciplinary program, and it seems to work really well. That way you get to take college level classes before committing to a track, and usually, it serves you well in your career to know something about the other kinds of Engineering. As you get closer to graduating, you can look at different college programs to find one that works well for you.
Regrettably, I can offer little direct experience, but at Dartmouth I know several engineers who prevailed despite learning disabilities. The bottom line is, if you can learn the material, at your own pace, as long as you end up understanding it, you can succeed as an engineer.
Nanotechnology is an interesting field because it so often involves collaborations between investigators from different backgrounds. That said, I think that most nanotechnology programs are centered in Materials Science/Engineering. To start your studies, you will need to take math, physics and chemistry. When you take these basic courses, I think that you'll find your interests will become more clear -- you may want to emphasize one discipline over the others. If the connections between the courses, and their potential applications get you going, then Materials Engineering might be just the right thing for you. Don't be worried about not knowing exactly what you want to do yet, but consider attending a college where you don't have to choose your major very early on. But do keep going in math -- it is important to all science and engineering disciplines!