If you already mailed your return, you cannot e-file it. It will be processed as a paper return. 

@ echeveste wrote:  " I chose to mail my tax return and now i want to e-file. i don't see an option to do that."

You said you made the choice to mail the return, but you didn't say if you actually DID mail the return or not.  Did you print, sign, date, and physically mail it?   If you did not actually mail the return, we can tell you how to open the interview back up, change the filing method to efile, and submit the return by efile.

We can tell you more about how to do that once you post back explaining more.