The first thing you should do is realize that you are in the same boat as just about every other college freshman on the planet. Please, don't sweat it. Most colleges don't actually require you to declare a major until your sophomore or junior year. You can always change majors if you decide you don't like your choice. You can even choose multiple majors or minors. However, the sooner you settle on your major the better chance you have to graduate on time.
The next thing you should do is consider major or intended area of study as a strategic application tool that can help you get the edge on getting in. You can improve your chances of being accepted if you let them know you are interested in a major that isn't popular on their campus.
For instance, if you want to go to MIT then you have a better chance of being accepted as a history major than as a computer science major. MIT has way more applicants interested in computer science than history. They want to maintain a solid history department so "all things being equal" they will choose the history major over the computer science major. (They are unlikely to admit this so you'll have to take my word for it.)
The good news is that after you are accepted as a history major you can switch to computer science without too much trouble. When you apply, make sure your application reflects your passion for history and not computer science. Heck, you may actually decide you like history!