GSTR1 AND 3B

I have filled GSTR1 and also submitted return. After it I realized that cess amount has to be zero but wrongly whole get amount written on that column becoz of which their is 11 lacs difference of tax occurs. Please help me with an option as I have to file 3b return and 11 lacs Demand occurs what to do to revise GSTR1 return... plz reply asap