I don't know why you have to maintain a 4.0, sounds like you have issues with yourself and being a perfectionist? C's are fine in college, I got straight C's my first semester, a "perfect" 2.0 :-) I graduated on time from University and have a couple of degrees; grades aren't going to make that much difference anymore than your high school grades do to you now. Keep going, don't worry about the C's; you cannot be perfect in all subjects (and you wouldn't want to be! Like my stepmother said when I brought home all C's, she didn't know what I was good or bad in; school grades just say you are good at school work, not "life").

If you Get A-C's in your City College classes, you can transfer easily to any other college because you have genuine "college" classes you took! It's not like getting into college where you had to have high school scores that were really good (because college is different); you are "in" college and can usually move around fine as long as you at least have C's. There are many more classes to go, concentrate on doing your best and learning what you want to learn and quit worrying so much about the grades; it sounds like you are doing fine!