Is it best to withdraw from this class?

I am taking this math class and I am in a situation where I need to get over a 80% in the class to pass. I never really had this problem before but I just am not really doing well this semester. I don't know if I could do it. My final is tomorrow and it's cumulative on material I have not picked up. What is better to drop and retake a class, or try to take the exam, fail, and then retake it?