i have exported goods and filed shipping on payment of IGST, But while filing GSTR1 & GSTR-3B i have wrongly mentioned it as without payment of tax. I commited this mistake from june,2017 to August, 2018. How can I rectify it?. The Igst amount cost upto 45 lakhs. Do i need to pay the 45 lakhs in october months 3B ? If i did so is there any possibility to get the IGST amount as refund?