full price paid

I purchased a land by an agreement to purchase from owner . I have made full payment but not registered it in my name due to paucity of funds . Seller has given full-payment-received-certificate . It is self-acquired property of seller . 

Can I face any difficulty till registry is done from seller or his heir (although it is seller's self-acquired property) .

what can I do meanwhile to secure my right so as to avoid any problems .