Don't take this the wrong way but...
80%-85% accuracy on SC is pretty damn good.
This means for every 10 questions, you miss, at most, two.
Most people who struggle with SC have a strike rate of 30% or 40%.
You simply need to identify WHY you are getting the remaining 15%-20% incorrect and move on (as noted in the post above)
You could check the strategy thread (link in my sig). If you've read the
MGMAT SC book, you likely know this strategy. Take a look and see if it helps.
You're doing great. Calm down.
I have attempted more than 250 questions now. I religiously go back and internalize the topics that I make mistakes in. But, even after, I am unable to breach that 85% accuracy and move up!
Is it concentration? Stamina? (I solve about 3-4 sets of 20 questions in one sitting)