Parking not mentioned in agreement of sale

Sir/ Madam, I am buying a resale flat and have entered into an Agreement of sale on Rs.200/- Non judicial stamp paper. This Agreement is not registered or notarized. I have bargained the deal and intended not to take car parking to suit my budget. The seller accepted as he could use this parking for his own purposes as he has another flat in the same building. So there is no mention of car parking anywhere in the Agreement (originally mentioned in the sale deed of seller and that Document number is mentioned in our Agreement). Now I feel that I better have a car parking but the seller is asking some amount to mention parking in sale deed where in I am not in a position to pay. What shall I do? If the seller executes the Sale Deed without mentioning Parking, does the Parking belongs to him or me. Kindly Advise. Mr. Varun Kondi