Cancllation of booked flat

Hello sir, I have booked flat in march 2014 in pre lunch offer. The cost of flat is 2043500/- After some time my builder arrange under consruction loan for me for rs 1690000/- and withdraw the fund from this loan 1390000/-. I paid rs 240000 as margin money. My current total payment to builder is 1630000/-. I also started payment to bank with full EMI of loan of rs 1690000/- since last two years. I already paid 365000 to bank as EMI. In march 2016 the property is ready my builder inform me to make sale deed but due to my fiancial week condition I am not able to pay more payments towards stamp duty charges and other service tax legal charges approx 380000/-. I request to builder that I am not able to make payment so please cancle my booking. Builder is ready for cancel the booking with 10% cancllation charges it is legal? And also builder informed me as tripart agreement they make payment to bank for outstanding principle amount. But the interest part of loan is 287000/- which I need to forgot. Cancel charge loss of 10% payment is 163000/- so in sort with interest my loss gone upto 450000/-. How can I fight legaly with the builder to reduce my loss to net 5% cancllation charges which is 81000/- only. Please advise me as I have no option to other than cancllation of my booking. Please reply ASAP. Thanks in advance. Raju