Hi, assuming you would have covered all the concepts by now, I see either/both of the following two possibilities in your case (with regards to my experience)::
1: Pressure / Exam Anxiety
2: Gap in concepts revision
I can share with you my case. I started my preparation in May and started with SC only. In June-July I focused majorly on Maths and in July end picked CR and RC. In June and July my accuracy in SC reached 80% (reference OG-2021 , SC-1000), but now my accuracy has dropped to 60% (reference - GMAT Prep Mocks and OG-2021). The reason I noticed was I forgot the concepts which were earlier on my tips. It happened because of the gap in studies and revision of the concepts.
Ideally, revision of all that has been done should go on a routine basis.
In my opinion, depending on the time availability, one should solve 10-20 Qs each from SC, CR, RC and Quant on a daily basis.Keeping the concepts on the top of your mind recall is the key.
PS:: I have my exam on 16th Aug, and I am targeting between 660-710. Shall share the debrief if I hit my target score.
In your case, you need to know why a question went wrong. Was it because you forgot the concept or you did not know the concept?
I am sure you can have your answer. Patience is the key !!!