Failed to show sep 2017 sales bills in gstr 3b and gstr 1 but party claimed the itc in sep 17 3b

Failed to Show sales bill of 05.09.2017 of Rs. 10,00,000/- and Tax Rs. 180000/- the pArty has show the ITC in 3B amount and claimed ITC but i fail to show in Both GSTR 3B & GSTR 1 now i am ready to pay the tax along with interest the party told me to show the amount in August 2018 GSTR3B & GSTR 1 and in GSTR -1 Show the Date as bill given to me on  05.09.2017 and Old Bil Number  i want to know whether i can show the amount as party mention he also telle that governemnt has given time upto 30.09.2018 for firgit ITC and sale bills like mentioned above kindly clear it