i received a private message regarding this thread.

there are really only three pieces of advice i can offer here, and they are all fairly general:

1/
you really shouldn't think about your "score trajectory" at all, ever.
no good can possibly come from worrying about this -- as you have seen firsthand, the only possible effect it can have is to distract you from the task at hand and ruin your concentration/confidence.
you should try not even to look at the "percentile progressions" on the practice tests. basically, those are in there as a marketing tool -- we have found that more people will buy the practice tests if they have bells and whistles like those -- but, unfortunately, they tend to build the wrong habits. specifically, they encourage people to worry about score trajectories, to over-weight the initial few problems, and so on.

2/
remember that this is an exam on which it's ok to miss quite a few problems.
this is the nature of an adaptive exam: you don't have to get everything right, or even close.

3/
your mission is basically to treat every problem in the same way as every other problem.

good luck.