If the plane is twitchy there are only two things you need to do. the first is add some exponential to the aileron and elevator surfaces. That will soften the response near the center. Start with 25% and see what you think. Second is to reduce the overall throw on the surfaces that feel twitchy. If you aren't hitting the stops occasionally while flying, you have too much throw. Do the exponential first and fly it. Then start reducing throw a little at a time (maybe 10%) and test flying until it feels good. You reduce the throw by reducing the percentage in your dual rates. I don't mean that you need dual rates, but simply that you can dial back the throw on the normal rate setting that you fly with. Once you are happy with the throw, it's good practice to change the linkages if you can to get the same throw with the higher radio settings. You do that by either moving the linkage in closer to the center on the servo arm or out farther from the surface on the control horn.