Due of GSTR-1 is extended till 26th may and 3B is extended by 15 days or 30 days based on turnover. If not filed by this extended due date then late fees shall be paid.
Currently there is no penalty on late filing GSTR-1. For GSTR-3B there is a late fee but relaxation is given. If you do not file under that extended period then penalty needs to be paid