Builder delaying Sale Agreement

I booked a flat in a community. The project was launched that time and I paid the booking amount of 5% followed by another 10% with in 30 days. As per the initial booking agreement (on paper and not stamp paper), it was mentioned that sale agreement will be done after 20% of payment. Now, it seems builder is not getting some approvals from local Panchayat and hence slowed down the construction. The builder is not even taking more money and hence not executing the agreement. The initial booking letter states the possession date as Aug 2018 but I am worried now as I believe the builder will change the final date in agreement. I want to withdraw my booking now but the initial booking letter has a penalty in case buyer cancels the property. How can I cancel my property without paying any cancellation penalty as I am cancelling because: - builder does not have all needed approvals - builder not executing the agreement Can I pay 5% more amount and then give builder legal notice to either do agreement in 30 days or cancel my booking and refund me full amount?