What do you mean you filed before April 15 but did not mail? If you actually efiled and submitted it you are done. You don't need to mail anything. When you efile you get back 2 emails. The first email only confirms the transmission. The second email says if the IRS (or state) Accepted or Rejected your efile.
When you log into your account you should also see the status and if it was Accepted or Rejected, Started, Printed, Ready to Mail, etc. What does it say?
If you were suppose to mail your tax return you can try to switch to Efile
https://ttlc.intuit.com/community/e-file/help/how-do-i-change-from-mail-to-e-file-in-turbotax-online...
If you are getting a refund there is no penalty for filing after April 15. You can efile until Oct 15.
