I'm sure it seems like that, and I also worried about being part of that 3%. But, you've got to step back and think clearly about it. Did you do well in your clinical clerkships? The OSCEs you had during that time? I'm sure you did. CS is not much different than exams you've probably already had. If anything, it was easier than my medical school's standardized patient-based exams.
So you made a terrible mistake in putting together your Match. I remember reading about that, and I feel terrible for you. I don't know how many times I double-checked my own match list to make sure something similar didn't happen to me. But one thing going wrong has no bearing on anything else unless you let it. The only way you will end up in that unfortunate 3% is if you freak out, lock up, try to do a 45 minute complete H&P in a 15 minute visit, and get lost in a herd of zebras when all they're really testing is common stuff. I know it's tough to believe, but CS is there to make sure you're a competent clinician--not a genius-level one.
No more rescheduling; no more beating yourself up over things that you can't change. Walk in that testing center confident that what you learned in medical school translates into good clinical practice. You've already, based on your previous posts, studied/prepared more than 97% of other American medical students for this exam. Why would they pass and you not?