Hi amandaabr,
I’m glad you reached out, and I’m happy to help. I see that you scored Q49 on your latest GMAC practice exam, so I really would not say that Q45 is a total disaster, though I do agree that it is a fairly significant drop. Regarding the drop in your quant score, it’s quite possible that nerves, stress, tiredness, or a combination of all three negatively affected your test-day performance. However, it’s also possible that you have some lingering weaknesses that were exposed on test day.
In particular, given that you correctly answered only 60 percent of the Geometry questions that you saw, probably you could be stronger in Geometry, and given that you correctly answered only 20 percent of the Rates/Ratio/Percent questions that you saw, it seems likely that you would benefit from strengthening those areas as well. Yes, your state of mind may have affected your performance. At the same time, if you were stronger in those areas, you probably would have correctly answered more of the questions of those types that you saw, even if you were a bit anxious.
It may be that part of what's going on in certain areas of quant and in Sentence Correction is that you are arriving at correct answers in practice because the questions you are seeing when you practice are similar to questions that you have seen before, and then, when you take the actual GMAT, the questions are somehow different from ones you have seen before, and so you are getting tripped up. To the degree that the foregoing is an accurate description of what's going on, the solution is for you to develop knowledge and skills that are a bit deeper and more sophisticated than yours are now, so that when you see unfamiliar patterns in questions, you are better prepared to handle them.
With all this said, I’m confident with some further, smart prep, you can improve your GMAT quant skills and thus your GMAT score. Would you like some more detailed advice on how to do so?
Lastly, you may find it helpful to read the following article:
How To Increase Your GMAT Quant Score