I have my 3.0 Road Race set up with an short older Cinelli stem and could see this setup described as twitchy, but not to a degree that it causes problems. Maybe "sensitive" is the right word. I agree with the other posters who suggested you try a standard style stem, since this is cheap and quick.
I also noticed you have your saddle a few cm further back than mine. Perhaps this frame is too small for you to get the twitchy feel you're after.

Or, maybe I don't actually know what you mean by "twitchy." When it comes to matters of fit and geometry riders' preferences vary widely.