I have completed the Arun Sharma - Quantitative aptitude for CAT book twice but i cannot seem to score more than the range from 50-80 percentile in XAT quantitative section. what to do?

i think you are able to attempt 4-9 questions correctly, in such scenario its important to not attempt any question you are not sure about or based on your intuition. You can go through all DI questions from the previous year question papers.