28 May 2018
Make sure you considered in Form GSTR-3B as well. Because the tax payment is done through GSTR-3B only not through GSTR-1.
In case you have considered all the invoices in GSTR-3B but missed out in GSTR-1. You can disclose in next month GSTR-1 without any interest liability, since the output tax is already discharged through Form GSTR-3B.