A part-time job can, at best, give you some additional money for incidental expenses in college. Also, the number of hours you work will impact clubs you can join, or group projects you can be part of etc.
I am a little surprised that you want to major in IR but have no interest in studying abroad. The top universities will have a “Why us essay” and perhaps one where you have to articulate “why IR”? Have you visited any other countries besides India? For the T20 schools, you may need to show an interest and passion outside the list of standard clubs you have listed. It would help if you whittled those down and focused on what really matters and interests you.