1. Since the agreement to sell is devoid of proper stamp duty to Government and not registered in the Sub-Registrar's Office and only notarised, it is not a legal document and will not stand the test of law.
2. Moreover it is time barred and cannot be activated now.
3. Since the property is in your possession and moreover you have made full payment to the Vendor in 2009 itself, better to get the property registered in your name, atleast now, by paying some extra money to the Vendor.
4. I repeat that you cannot rely upon the 2009 document of 'Agreement to Sell' due to the reasons stated above and forthwith enter into a fresh agreement of sale with the Vendor with 3 month's time for registration or directly get the property registered in your name by amicably settling the matter with the Vendor.