Taking an extra semester to raise GPA I'm not sure if this is the place to ask about graduate admission, so please let me know if the question is off-topic.

I'm currently in my senior year doing my undergraduate degree. I recently made the decision to pursue graduate studies (M.S. CS), but my GPA is a bit low. I will graduate with a double major degree in international relations and computer science. My major GPA will be 3.1/4.0 (cumulative 3.3/4.0), and so I decided to delay graduation an take another semester to raise my GPA (retaking a couple of courses and taking one new one) and also give me more time to prepare for graduate admission as I felt I was a bit too unprepared. After the extra semester (and assuming I do average to well) my major GPA will be 3.4/4.0.

I took the GRE and did well (163V / 169Q / 5.5 AW), but felt that I want to invest as much effort as I can (since this is the only time I'll have, to raise my undergraduate GPA) and then apply when I'm better prepared.

Does graduating late reflect poorly for graduate admission? I wanted to use that time and take advantage of the fact that I'm taking fewer courses during the semester to work on other projects as well.

Any feedback is appreciated. Thank you!
In general, taking longer to graduate is not a problem. However, your plan of retaking courses rather than taking new courses is a bit flawed. If you take more advanced courses and do well, then your earlier performance on more basic classes is less of a concern. It might not bring up your GPA as much, but taking new upper-level courses (and doing research as you have suggested) will give you more to talk about in a SOP, strengthen relationships with faculty, and better prepare you to do research at a graduate level.