My tip is to relax and focus on enjoying college 
-Any of those three universities will be excellent prep for going to graduate school, so don’t worry about that. Congrats on the full tuition scholarship. I’d definitely take it.
-You may change your mind about loving school after you do four years of college I loved school and thought I would love graduate school just as much, but I totally didn’t.
-International affairs programs value work experience. The average age of students in these programs is mid-20s, and they often have 2-5 years of work experience between college and grad school. So, even if you want to go to grad school, your application will be a lot stronger if you work first. So do some internships in college - that will strengthen your application both for work and for grad school later. Then try to find employment in something IA-related.
-IA programs also value language learning, so select a language and stick with it through college. Studying abroad is your best bet, especially if you study somewhere that speaks the language you’re learning and you can at least get conversant in it. It’s a good bet to select a language that is relevant to the region you want to study or be in (e.g., if you are interested in West Africa a language like French or Wolof is a good bet). Critical languages are always good; take a look at the Critical Foreign Language Scholarship and the Boren Scholarship/Fellowship for an idea of what critical languages are and the kind of support you can get for studying them.
-You don’t really need to have research experience for professional programs (which international affairs is). It can’t hurt, of course, but if you don’t like research don’t force it.
-If you want to join a sorority, go ahead! You don’t have to put it on your grad school applications, and most admissions committees honestly won’t care. Lots of very successful politicians and international figures were in Greek organizations.
-There are some scholarships/fellowships for graduate school that you can apply for in your junior or senior year of college that help pay for graduate school. One that you may be interested in is the [Pickering Fellowship](Thomas R. Pickering Foreign Affairs Fellowship | The Washington Center), which is specifically for students interested in foreign affairs. It includes up to $37,500 in tuition for two years plus two summer internships, mentoring, and other perks. You have to apply in your junior year.
Another is the [Truman Scholarship](Before Applying), one that you also apply for in your junior year. You have to want to be a “change agent” and want to get one of several degrees, including an MIA. You have to have participated in certain activities, so take a look at the requirements.
Another is the Beinecke Scholarship. The Fulbright Fellowship program is another prominent one; the traditional program is for graduating seniors and graduate students to get money to conduct research in another country for a year, but they also have some limited Fulbright programs that pay for you to complete a master’s degree abroad and others that allow you to serve as an English Teaching Assistant abroad for a year. That’s good experience for an MIA program.
