I have given a sectional test for quants recently and one thing which has worried me is that whenever i attempt a question and find it familiar to solve but could not attempt it correctly and after the test i solved those questions with ease, I am unable to understand what is the exact reason behind this, how should i overcome this aa when i giving the test i found 90 percent questions familiar but hardly was able to solve 20 percent questions? I need help regarding this issue. Thank You

You are not able to perform under pressure which is very common. In my opinion, you should focus on 1 question that is familiar to you at a time and try to solve that completely without thinking about the time before moving to the next question.

I'm no qualified personnel to answer this but having faced the same issue I can assure you it's a mixture of various things
one being(this is a problem I identified in my prep) solving tough questions in general and completely ignoring the straight-forward simple silly things the question setter traps us in. its only solving these simple things that we first get to understand the question setter's brain and all the traps they set understanding these traps can help us be better test takers. I hope you found this helpful.
Good luck and stay consistent.