What went wrong?

I just took my first GMAT today and unfortunately am one of those bringing back horrible news. Compared to my practice tests, I completely bombed the GMAT due to my poor score on the verbal section. I did amazingly well on the IR and earned a perfect 8, my highest score. I also did quite well, by my standards, on the quant and received a 47, just one point lower than my highest practice test score. However, I got destroyed on the verbal for some reason; I received a 31 when I have been consistently scoring 38-40 on practice tests. My verbal percentile was actually lower than my quant percentile which completely baffles me.

During the exam, I thought that the sentence correction questions were incredibly difficult, about the same difficulty as the most difficult practice questions I had done (which in my opinion are the MGMAT questions) or even slightly more difficult. I felt pretty comfortable on the cr and reading comprehension during the exam and am guessing that I missed no more than 6-7 questions in those two sections combined. What confuses me even more is that I thought I had been doing very well on the sc practice questions. Just a little more than a week ago I finished the remaining sc questions, the ones towards the back of the 2017 og book that are supposed to be the most difficult, and correctly answered 29-30 of the last 32 questions. With that being said, I am wondering if anyone has any idea as to why the sc on the test seemed to be so much more difficult for me granted that I have found success on some of the most difficult questions in practice.