Most of the PSUs give a lot of weight-age to GATE score. Therefore, try to score good in GATE and don’t think about anything else. They will surely ask you about the gap, so prepare a valid and an authentic reason for the same. Do not criticize the College for placements nor the company where you worked/not joined. This will be the first question in every interview especially ESE interview, but there is no need to worry at all.

Feel free to ask me in the comment box if you are having any further doubts

hope you find it helpful

Good Luck!