Agreemeent for sale - delay in payment by Buyer

I have agreed to sell the plot of land during May 2015. Time for completing the registration is 3 months. It means Buyer has to complete the registration before Aug 2015. Whereas Buyer is not coming forward for registration since he is having problem with the arranging the remaining money. Hence registration is not completed. Now it is almost 11months deal is not completed. In our agreement for sale we have as follows: 1. If the Buyer does not come forward for registration before 3 months, he has to forgo his advance money. 2. If seller does not do the registration, then he can approach the court for registration. I am doing verbal follow ups with Broker and buyer for registration. I do not have any proof that the fault is from Buyer's side. Now we have agreed for registration after one week which 28th April 2016. if Buyer does not fulfill his promise, I would like sign off the cancellation agreement. Please advise on the following. 1. Whether the clause in the agreement for sale is sufficient for me to not to return his advance money since he has not come forward for registration? 2. whether I need to sign the cancellation agreement even after having cancellation clause in the agreement?