Once the agreement to sell has expired the parties become free from the terms and conditions of that expired agreement. If they want to abide by those terms and conditions, they have to execute a fresh agreement on the same terms.
In the current situation, the buyer cannot compel you to perform that agreement to sell even by the court. The agreement to sell neither confer any right in the parties nor create any charge upon the property.
In absence of any right and liability accrued from the said agreement you are free to sell that land to another buyer on the better price. If you want to take a judicial decision on that agreement you can file a declaratory suit for the declaration that the said agreement became void. Thereafter, the buyer cannot stop you from selling that land to another buyer.