You are at liberty to cancel the agreement and seek refund of money paid by you 

2)builder can charge you 2 per cent cancellation charges 

3)you are entitled to refund of stamp duty provided registered cancellation deed is entered into with the builder 

You can claim refund after cancellation as per rera rules. You may have some charges deducted but the major part will be refunded 

if you intend to cancel the allotment and agreement then the cancellation terms will be provided in your agreement itself

so please check your agreement for that

as regards refund of stamp duty there is a provision in the Stamp Act using which you can apply for refund of stamp duty within the stipulated period after execution of the deed of cancellation

as regards refund of GST, you will have to consult a GST practitioner 

if you have a buyer who can buy your rights under the agreement, then you can try that as well since that will save you from doing all the procedures for refund of stamp duty and GST and will also avoid payment of penalty to the builder for cancelling the unit without any fault of the builder 

Cancellation is definitely possible and to know the process and terms and conditions of cancellation, you will have to refer to the termination/cancellation clause in your Agreement to Sell. It is very much possible that the builder will forfeit some money from your total deposit in lieu of cancellation, but he has to refund the rest. Pls show us the Agreement to Sell for better opinion on your query. 

You can very well cancel the agreement to sale by sending a communication in writing to the builder even if it is RERA registered project. 

You take steps as suggested,  if the builder is reluctant or refusing then you can approach RERA with a complaint against the builder. 

Earlier, builders used to charge up to 10 per cent of the total cost of the house as cancellation charges but according to the new rule, it has been lowered to just 2 per cent. This means that if someone cancels the booking of the house, he will have to pay only 2 per cent of the total price as a loss to the builder

Dear client, The RERA Act allows the homebuyer to withdraw from the real estate agreement, regardless of whether the developer is in default. In such a case, the developer is required to refund the amount paid by the allottee within the time frame specified for the allottee's withdrawal, after deducting the amount paid for the allotment and any damages caused to the builder.

- There is no provision in the law to forfeit the booking amount for the cancellation, and the deduction is done at the builder’s discretion.

- Hence, legally, the builder cannot deduct any money out of the advance payment you have made for the booking till the time; a builder-buyer agreement is made and registered with the sub-registrar.

- Further, A builder-buyer agreement is not created until the buyer pays at least 10 per cent of the property value.

- Further, as per RERA, home-buyers can cancel allotment of the apartment booked with a builder at any stage even if there is no default on the part of the builder . The builder is bound by law to return the money collected from buyers within 45 days, after deducting the booking amount.

- Hence, if you have already paid 10 percent of the flat value, and the said agreement signed by you , is not registered in the office of the Registrar , then you are liable to get full amount refund paid by you ,even there is a clause present in the agreement for not refunding  , and if the said agreement is registered , then builder has right to deduct booking amount from the paid amount. 

- Send a notice to the builder to cancel the allotment and to refund the money paid by you. 

- If, builder not refunding the same ,then you can file your complaint before the Consumer court , and thereby prayed for the refund of paid amount with interest.