I was just wondering if once I pressed submit on my 2017 tax return, did that automatically e-file it or is that something I physically needed to do separately?

I guess it isn't as hard to e-File accidentally as I thought it was.

No -- once you press "submit" it is just like dropping your tax return in the mail box.  It's done.  You should get a response from the gov't in a day or two telling you whether or not it's been accepted.