Dear Annu, 83 PERCENTILE is not a good score because you can't qualify for jee advance with these marks as per you mention you did not give proper time in study. So for your kind information, you have to secure up to 95-97 percentile for NITs.If you feel you can achieve it if you give proper time then take your chance as per the psychology a human being can do anything if they thought it and implemented properly with focus, so be focussed and do hard work you can achieve it for sure and practice lots of question that make you succeed.

Best of luck Annu