skipped adding a bill last month

Hello everyone !

I was just wondering what if I filed my GSTR-1 of January month and skipped adding one/few taxable invoices ?

The portal shows a message "return once filed cannot be changed" !!

I can't add that invoice in the month of February either bcz it doesn't accept that invoice date of another month ...

Secondly , what if I purchased taxable goods ...the invoice was issued from the supplier's end on 27th of January (& he displayed that in his GSTR-1 of Jan month) and goods reached me on 3rd of February ? Practically from my point of view , I will recognize that purchase invoice on/after 3rd Feb as purchases ,once I get satisfied after receiving the delivery of goods ...GSTR-2 is not meant to be filed till now but still..what will be the implications if I show the same in GSTR-2 of next month ?

Thank you.