Need some assistant for cancelling agreement for sale

I booked a flat, provided cheque , it is written it is shali land instead of vastu. However I didn't know about this so signed it. I got to know about these things only after when sbi didn't want to give me home loan since it is shali land. I already informed builder that I need to cancel this agreement due to some financial crisis. He was not at all happy with the decision but however after some discussions he said he will return me the cheques and will cancel the agreement. How I will know this agreement is cancelled, will there be any cancel agreement on a new stamp paper done? Also when I issued cheque I didn't have much fund and it was already communicated to the builder, he said he will present the cheque only when I let him know. It is mentioned in the agreement that builder will provide any documents requested by me but he hasn't done so when asking for mutation and land conversation from shali to vastu.