Refunding prior to agreement

respected sir,

i have booked a duplex  on 29th oct. 2013 in cash down plan and 6.5 lac Rs.,but  the AGREEMENT IS NOT YET been signed with the builder.But due to some personal reasons, I  want to cancel  my booking  and want full refund .but the builder is saying that  10% of total consideration (39 lac) will be deducted . 

so what is the provision of law? and what should  i do ?

regards r.k