Gst mismatch and penalty?

Ajay (na) (55 Points)

11 October 2017  
If I have filed NIL gstr-3b for JULY,AUG,SEP

but Now I come to know about Input services Bills of JULY,& Aug.

Can I file for INPUTS in GSTR-2 now?

will there be any penalty and how much?

Can I Revise my GSTR-3B?

Pls help