Need clarification regarding gst input credit

Firstly, try to convince your supplier to issue you a credit note in the same month, so you can post with less amount.

If not, he will pass is paying more tax and passing higher credit, if you accept that in return, it will be ok...

There will exist a mismatch only if the buyer claims more ITC than passed by seller. SO in your case you can modify the same and the seller will accept in GSTR-1A.