Please Help: capital gain- short term

a lady was allotted a plot by NOADA authority in istalments. She sold the plot to her daughter in law and entered into an registered agreement to sell. A cash consideration was shown in that agreement. No possession has still been given to the allottee. Now the parties are interested to cancell the agreement. Now the querry is: whether it is possible to cancell the agreement.If yes- what precaution should be taken. What will be the position regarding short term capital gains.