tax amount entered wrngly

any Retrun of GST , once it was submitted then you can not able to rectify during said period... you have to wait for next return for rectification accordingly ... Don't worry .. you have to calculate perfect GST payable and deposit the same... Also fill the GSTR-1 perfectly and submit .. also File .... There is no temporary provision for penalty of mis declaration at GSTR -3B for July and Aug,17