august month return filled,but two invoices missing,

iam ready to add missing two invoices in gstr 1,, already have it excess ITC , my question is 1. now iam going to file gstr-1 for the month of august ,any late fee Will come or not. 2.What about the difference amount added in gstr 1 additional invoices.But 3b entered amount is not matching,after adding two invoices? the how it solve. 3.input tax available for the two invoice tax amount carry forward for next month or not? but input available month is august. September month return is also filled. how is possible ?