Ready to Mail means that you have to print, sign, date and mail the tax return to the IRS, it was not e-filed.
You can change from mailing the tax return to e-filing the tax return by following the procedure in this TurboTax support FAQ - https://ttlc.intuit.com/community/e-file/help/how-do-i-change-from-mail-to-e-file-in-turbotax-online...
There is no penalty for filing after the due date if there are no taxes owed or there is a tax refund.
