I want to cancel my flat booking whoose possession is ordered

I had booked a flat and paid full amount of it. Now the builder has offered for possession but i due to family problem i am unable to register and so i wish to cancel the booking as sale deed is still not executed. I am ready to forgo all interest, all gst taxes and also ready to deduct 15% of booking amount. Still builder is not ready to cancel. My booking is of 2016 before Rera, BBA has been signed but not registered. In BBA buyer can cancel booking only within 60 days is written. Builder can cancel any time after deducting 15% of earnest money. In BBA it is written that no one can change project name but in Rera builder has made minor changes like residences is changed to residency in rera In BBA builder has to vacate any loan on plot before handing possession but builder has not closed the loan on the plot. In BBA date if possession is 36 months and 6 months grace from agreement date but force major clause, sunday, govt holiday not included in calculation. builder has given possession in 48 months instead of 42 months so will force major clause be in builder favor. Pls. suggest.