In the present case scenario, you should serve a legal notice to the builder asking him to do the necessary acts and then you'll remit tye balance amount.
Also state that he cannot cancel the contract as more than 80 percent same consideration and he hasn't performed his part of the agreement.
Give him 10 days to do the needful, if he doesn't, then you can proceed to file a complaint in consumer court seeking damages for delayed possesssion by the builder.
Feel free to call for any other doubts or queries.
Regards,
Siddharth Jain.