Hi Archie,
Relax and breathe! I was feeling exactly the way you were and taking the PMI mock did not help. I scored 70% in it and the result was 'failed'. It crumbled my confidence completely. I found the PMI Mock was vague and not of as good quality as Prepcast Simulator or even Oliver Lehmann.
On the simulator, my scores were 75%, 78%, 79%, 78.5%, 82%.
As you will read from my feedback below, even though my prep time was short, I don't think delaying my exam (even if I had the time - if the pattern of the exam was not changing), would have helped. The exam is what it is. I did get confused on a few tools and techniques, so make sure you have that on your tips. For example, you project is delayed blah blah, how should you inform the sponsor and senior executives - gantt chart, burndown chart, etc.
Hope this helps!
Best of luck

I am sure you will do well. Remember not to exhaust yourself the last 1-2 days and take it easy.
Harleen