Wrongly avail input - Goods and Services Tax - GST

I have recently received a departmental notice under Section 74 for the fiscal year 2017-18, citing an inadvertent claim of CGST and SGST input instead of IGST. I promptly rectified this in my annual return; however, due to the absence of any purchases involving CGST and SGST input in the specified period, the correction was not reflected in the GSTR-3B . Seeking your guidance on the best course of action to safeguard my case.