It's a common problem.
Also the reverse: people who only play online will make silly blunders when playing on a real board.
But eventually you'll adjust and play at the same level on each. You've only played ~20 games here so it makes sense to me you're not completely adjusted yet.
If you have managed to play a full game playing yourself then respect.
If you have managed to play a full game playing yourself then respect.
It's even harder to you do your best... because it's tempting to favor one side at some point.
If you do your best it should be a draw (or close to it).
(I haven't played myself in years though... doesn't really make sense with opponents available all the time)
Another common problem is playing with yourself. It seems like good practice at first but eventually you become strategically blind.
Dude, this is a Gem! I am still laughing 
I once had a practice/teaching game in which I played my moves and my opponent's (a relatively inexperienced player) moves. And I lost!
I can't, for the love of God, play a decent game of chess in here; however, when playing with a wooden chessboard, with another person in front of me, I can play a decent game. I'm getting frustrated, as a lot of the games that I have lost here, is because of really stupid mistakes far into the game, mistakes that I would've never made in an in-person game.
Has anyone had any trouble adjusting from real life, in person, games, to playing in a 2D computer screen?