Excess ITC shown in GSTR-3B

I added a purchase bill with Input IGST amount of Rs.118. I have shown Rs.118 under "Eligible ITC" in GSTR-3B of 10/2020. But later when I noticed a mismatch with the GSTR-2, I found that, as per the vendor filed invoice, the Input IGST is Rs.115 only, which means I have shown excess ITC of Rs.3. So, I have reversed the ITC amount of Rs.3 in GSTR-3B of 03/2021. Now my query is, should I correct the purchase bill too or keep it as it is? Whatever it should be, it must be according to the GSTN regulations.

Please help! I'm confused.