I agree that you can call the song itself finished, but the recording does sound like a demo. GFS recording advice is worth following as far as recording acoustic guitar is concerned, but you don't have much excuse for "only a computer mic" when you can get good large diaphragm mics so cheaply- and you can justify it by the fact that everyone here thinks your music deserves it!
As far as arrangement goes, I'm not sure about harmonica. I'd use a Steel guitar, but that's because I play one. Whatever you added, I feel you do need a bass, and a second guitar line, capo'd up on 5 would be nice and it would add a bit of sparkle at the top end. How's you vocal harmonies? I can "hear" a nice country harmony in the chorus.
Finally, you need to investigate the thorny subject of mastering. Your final levels are low, even for an acoustic song.
Cheers
Dave