Change in external layout of flat after "Agreement to sale" registered

Hello Sir/Mam, I have purchased a 3 BHK on 8th floor in Pune wherein builder mentioned 1 terrace in Living room and another terrace in children bedroom for even floors. For odd floors builder has given second terrace in master bedroom. My agreement is already registered and it has flat layout showing second terrace in children bedroom. However now builder informed me that they have changed the plan wherein they shifted all floor's second terrace to master bedroom and there won't be any terrace in child bedroom now. This is not acceptable to me as I needed terrace in children bedroom as per my agreement. My question is whether builder is allowed to do such changes legally? If allowed and if I want to cancel my booking, how I should go about it as I have paid amount to builder, disbursed loan from bank, paid TDS, stamp duty and registration. Will I get refund of full amount? Also if i continue with the booking, will it have any impact as my agreement has different terrace layout as against actual layout? Kindly suggest.