Should I change my major to something more useful yet less interesting to me l if I already secured an internship in that field? I'm currently majoring in Political Science with a computer science minor. I managed to secure an internship with a large, multinational software company for the summer of 2020 as a data analyst (more on the business side than CS side). I was thinking about switching to Economics for more rigorous mathematical training and either keeping the minor and graduate on time or dropping the minor and graduating a semester early (the minor is 22 credits for some reason).

The thing is, I don't like econ. I am in intro Micro now and it's by far my least favorite class. However, this is likely not helped by the fact that the teacher is not the best, it's a 300 person lecture and from 4:30-5:45 twice a week. However, the higher level applied mathematical parts of econ intrigue me even if they are hard. I think the analytical classes would benefit me a lot paired with computer science.

Anyway, my question is should I still switch to the more useful major I don't love as much and possibly graduate late, or stay where I am since I got an internship with a large company that is gonna help my resume a lot and rely on that experience?
There is hardly anything worse than spending your life, or your efforts, on something you don't love. 

The mathematical training in Econ will be a bit limited if focused. You might do just a well taking some of your elective courses in math. That would also support your CS minor. Statistics would work with Poly Sci also. 

Don't think "useful" unless it is an economic necessity. You are well placed to do something that you find interesting as well as rigorous. Too early to make such compromises.