Have you been fitted for this bike?
It sounds like your either not flexible enough to get the proper extension/reach needed to shift properly (work on core strength), your bikes length may just be too long for you (need seat moved forward/stem adjustments-- etc), or you may need smaller shifters for smaller hands if you don't already have them.
You say the bike is more twitchy, but unsure if you're comparing this to a hybrid, or you had narrower bars installed on your road bike when you had the breaks modified, and that's the comparison.
I did notice my road bike was much more twitchy/responsive compared to my road bike and just something that I'm adjusting to. I'm new to road bikes as well and just bought my first roadie about three weeks ago. On my first ride my foot slipped on the pedal and just a slight shift in weight sent me across the road, about five feet off my line, and I nearly crashed. It was really scary, but I recovered, so I have a new appreciation for the bike and my ability to handle the bike.
One more thought. You said you had break levers installed on the flat portion of the road bars, so I'm wondering if your hand position may also be affecting how twitchy the bike is... the closer to the stem your holding your hands the more small movements/adjustments are going to affect the bike.
Being up on the hoods instead of down in the flat part of the bar will mean better control over the bike. I've also read that, while I'm not comfortable enough to ride down in the drops, it's the most stable place to steer from while descending a hill.
Good luck!!!
Shannon