During my first 3 semesters or so I got some Cs which kinda hurt my GPA. My GPA is now a 3.43 and it will probably be around a 3.5 when I graduate. I am considering retaking some of the classes I got low grades in to improve my GPA (like a couple humanities courses, intro to C, and economics). Should I even bother? Is a 3.5 looked down upon by grad schools that much where it is worth it to retake this stuff or should I just take more engineering and physics courses?