Is it mandatory to squareOff MIS Short Options on expiry day?

I have shorted an OTM option using MIS type of order on the morning of Expiry day. I am confident that the position will expire OTM by end of market time. Do I still need to square it off before 3.20 PM because its an MIS product or will I be charged auto square off charges or will it expire worthless & I can pocket the entire premium?
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