GSTR1 March 20 due date extend

No........... but will definitely extend.
(wait for Notification, Already there in press release)

GSTR 1 return for the month of Mar-20 will be extend to 30th Jun-2020. Already press release issued by CBIC.
Wait on further notifications about the same...

As per Notification No. 33/2020 - Central Tax, dated, 03.04.2020, the due date for filing FORM GSTR -1 for the month of March, April and May 2020 for the Taxpayers having Aggregate Turnover of more than Rs. 1.5 crore have been extended to 30th June 2020.

March : 30.06.2020.
April : 30.06.2020.
May : 30.06.2020.

Late Fees levied u/s 47(1) of the CGST Act 2017 has been completely waived off, if the Statement is filed within 30.06.2020.