If your Federal return has been accepted, here's how to go back and efile the state return.
If you log in, and the interview is closed, scroll down the Tax Home page looking for a link "Add a State." That doesn't really add one, but will open the return interview back up. Once the return interview is open, and you have a full left column menu, you can go to the State tab to continue working on the state return, if needed. When finished, run the State Review to be sure all is in order. Continue to the FILE section, and choose to only efile the state return. Print out the state return before filing if you want to review it. Be sure you go all the way to the final screen and click a button "Transmit My Returns Now." Watch for an email saying the state return had been transmitted. That should be followed by a second email in a few hours (but less commonly up to 48) that the state return was accepted or rejected.