Under pressure, everyone has moments when they feel unable to cope, but sticking to a realistic revision plan will keep your confidence afloat. If you're charting your progress in this way, you're less likely to get intimidated by the workload and end up throwing your hands in the air.
Don't give up - packing it all in at this stage is basically the easy way out. Sure, it'll stop you feeling stressed, but think how you'll feel on the other side of the exams. If you think you'll look back with any sense of regret, then it has to be worth giving it your best shot.
Even if you don't get the grades you want, taking exams keeps your options open. You could retake, consider other courses, or look for work. Whatever your results, however, something's better than nothing.
If you think that you've failed...
Even if you did freak out in the exam hall, there's really no need to panic now. First of all, it's perfectly natural to feel some apprehension in the run-up to the results, and often people find their worst fears are unfounded.