What happens if option is not squarred off?

I had buy ongc 320 put @ rs0.20 on expiry day but just before the trading hrs. NO one was there to buy the option so that i can square off my position . In this case what will happen. Whether i have to exercise that option or it will lapse.

If ONGC closes below 320, your put option gets automatically exercised. If it closed above, it expires worthless. If it gets exercised, you have to pay higher STT, check this: http://zerodha.com/z-connect/queries/stock-and-fo-queries/stt-options-nse-bse-mcx-sx