Under construction Flat Cancellation

1 Year Ago I Had booked an flat in under construction projects , as while negotiation with the rate is concern how much would you can pay , I told him that we can arrange upto 20lac then he has finalised with the price , we book the flat with an token amount of Rs 10Lac by cheque , and respected 10lac will arranged & give , but any how we could not arranged the amount , so builder had changed the rate by , but he had not informed us that if you pay 20lac this will be the price but if pay less then the amount then price will increased. What we had decided to now if he try to increased the rate we will cancel the flat & took all my money back , when we had approached him he told that if you cancel the flat then we will refund money 9.70Lac insted of 10lac , as then had paid the service tax to govt. & all money will be paid after 45 -60days. What I want to say that the builder also used my money for 1years then he has to pay me the interest too of my 10lac. Is iam wrong to my approach, whats the way to recover my money from the builder,. Kindly suggest me some opinions.