Hello there, don't go into the "quitting" mode. There is still plenty of time this semester for you to succeed. You only have 2 pre-reqs left, and you will be set. I know that perhaps it might seem like you can't do it, but don't doubt yourself!
It happens to all of us, and the best thing to do is keep a postive attitude and find an alternative way for you to study. Perhaps try changing your studying habits, look for outside resources (i know youtube has excellent vids) or work less hours? Please do not think that you can't be successful in nursing school, because you have already showed yourself that you are capable of getting high A's and B's as you previously got last semester. With every little challenge that we overcome, we tend to slowly expand our circle of capabilites. I am sure you will suceed in nursing school, as you will be used to your extensive studying. Keep moving foward towards your goal and don't settle out just because you were simply too anxious. I was in the same situation as you when I was taking A&P and Chem, and I decided to drop A&P, because I had a "B" average so far. It was on the skeletal system later that I knew I did horrible probably around a D, so I decided to drop. I later had to take the class all over the next semester. I got an A the second time, but I now realize that perhaps I would of been able to pull of an "A" the first time, since I still had 2 exams left, a few quizzes, and 2 lab practicals. I even later found out that the professor gave out an extra credit opportunity. :-/ Anyway stick to it, and maybe go to office hours to check out your previous exams. What is the material that you quite didn't grasp? In science it's important to not get behind because, everything haunts you down from the beginning. I also recommend forming study groups talk to those A students in your class, and let them know you are very hardworking. Study groups are an excellent tool to share resources, and feel more comforting in class. When you feel more comforting, you feel much more confident in participating in class and asking questioons! Good Luck!