If you aren’t confident taking one hand off the bar to signal a turn, I have to wonder if a different stem would make any difference; it sounds like other geometry is contributing to the perceived twitchiness. I don’t know how many miles it will take to acclimate, but definitely more than you’ve put on it so far. My advice would be to go out and “play” — stuff it into some corners, put your weight way forward and way back, sit on the top tube, ride no-hands, bunny-hop the train tracks. Bend the thing to your will until you feel at home on it.