Hey,

Firstly the answer keys available immediately after the exam are released by various coaching institutions and not by the official website. So sometimes it happens that some questions have contradictory answers. So the answers vary sometimes. 

Or there may have been some miscalculations from your side while matching the answers. Or you may have bubbled wrong options in the OMR. Because the answer sheets are checked with extreme caution by the organisation conducting NEET. So there cannot be any fault from their side. Hope it's clear.

All the best