Whether I can resell my land to others before settlement with present buyer

Dear Sir, I have a flat registered on my name & my wife,s name in karimnagar.My uncle has made agreement on 100rs stamp paper on my behalf in august and took some advance.In that agreement it is written that land as per document xx of xx square yards will be sold as a whole for the agreed price .Later after 15 days I went and he has paid some amount and we have made agreement that with in 90 days as per dimensions if gives money land will be registered on his(buyer) name. But he has not responded till 80 days .After so many calls ,on 82 nd day he came and said that land is not as per measurement .Then we mutually agreed to measure the land and close the deal in couple of days. Now he is not responding to our calls.Now 90 days is over. In document it is mentioned with in 90 days he has to pay as per measurements.If he fails to pay what is to be done (those details are not there in agreement).Now as the 90 days are over whether I have the right to give his advance back and retain/resell my property.?( It seems he will take more time and once he get good buyer to that property he will come to me and pay less money saying dimensions are not as per document.) Pls advice