Do not drive yourself crazy trying to figure out how the test is scored. What you need to focus on is how you did vis-a-vis other people who took the test. That is all that matters. For most top programs, they look for you to score around the 80th percentile on all sections of the exam. Anything beneath this can be troublesome.
Also, one of the reasons you study so hard for the exam is to figure out those areas you excel at and those areas you do not excel at. From my experience, the test pretty closely mimics the actual test - meaning if you are having problems with one aspect of the test, chances are this part of the test will also be problematic on the actual test. So, if you do not get the score you want, focus on addressing your weaknesses and you will see a marked improvement in your score.
Good luck on the exam and focus on doing well on the test - not the craziness that goes into writing and scoring it.
Manhattan Review