Good choice :o And yeah, best of luck :x paying is something you should definitely keep in mind, look into work study and DEFINITELY apply for every single scholarship you can find. There are a lot of weird ways to have others pay for college lol, just try to avoid loans if possible because those tend to hurt later on >_>
You have plenty of time and if you're setting your sights on a school like Duke you probably shouldn't be TOO nervous lol, but that doesn't mean you shouldn't get started now. It pays off to give things a trial run early, I suggest that you start looking into both the SAT and the ACT and take some serious practice runs through both exams to see which one better suits you. The ACT is an option people don't talk about much, and it boosted my SAT score by an equivalent of 270 points, so I tell everyone who's applying to check it out