C form assessment w,r,t different tax rates

we sold goods on c form to goa(2010-!!). now they cant issue c forms due to their problem. we have sold 5% and 14.5% products availing c form concession.i want to know whether we have to pay the difference of the tax according to the tax rate of that product (say 5-2=3%) or 14.5%-2%=12.5% on all sales done in 2010-11 . thanks,I have sent the same enquiry earlier