Regarding your practice score, I find the UWSAs over-predict by up to 10 points, so in that sense I would not "trust" that score. I would focus more on your NBME scores to set your expectations, although those scores are more variable, you don't want to lull yourself into a false sense of security by relying on a practice test that inflates scores (unless you take that into account).

Unfortunately, there are no reputable explanations publicly available for the NBMEs. I would not spend time scouring forums to try to find them, as those that existed previously have been rife with errors. We advise our students agains them, and instead focus on 1:1 teaching of the concepts underlying the NBME questions a student struggles with. You're right to do all the NBMEs, but I would advise a study group or near-peer tutor over un-verified anonymous explanations!