First of all, it is absolutely feasible for you to get into a top institution (master's) in the United States. I graduated with a bachelor degree in a subfield of computer science in 2012 and forwarded to a reputed graduate school. I am very sure I knew less than you now about what is political science when I was 21, but I had interests and faith. So be confident.
Second, it would really make a big difference if you manage to get a master's in a reputed policy school or political science program. To name a few, GTown, JHU, UChicago, UCSD, Duke, NYU. It would also help you discover your real