Cancellation of flat

Hi, I have booked a flat and have given 15% booking amount. After 2 days of the released of cheque, I have given a request to cancell my flat and Builder said that okay but we will deduct 15% of the given amount and It will be back to you in next 3 month. Though I have read my application form carefully and no where it mentioned. Except application form I have not signed any where and no agreement was made between me & buider. Please suggest me on that and how I can recover my money soon.