Property Delay/change In Size

I have an apartment delayed by 2 years and the size of the apartment is smaller than what was signed in sale deed. 1. Builder claims RERA has given a 1 year extension due to Covid. Is this true? Delay penalty in agreement say Rs 5 sqft/- per month of delay. 2. How should the penalty for change in sqft (which is now reduced in what has been constructed from what was in sale) be calculated at what rate, same for principal? I heard it is 12 pc/annum from date of booking? Is this correct? 3. He is asking me to take over for interiors next month no OC yet 4. Property selling almost 65-70% more than what was purchased for. He is ready to sell for me but is quoting only 18-20% more than what I purchased for. Impact? Best legal course of action? How do I proceed here? I want to sell it/recover maximum money. I heard from RERA that you get 10pc penalty? Is this per year from booking? 10 years have passed from date of booking.