Competition guys do have switches that we turn on or off, called flight modes. The best of us don't turn these on and off all the time...that's too much work load, especially in the heat of competition. Newer guys do this though because they don't have enough experience yet to tune their models aerodynamically. If the model has a very slight tendency to roll out or in, mixing in a little (1 or 2%) opposite aileron with applied rudder is common for many, even seasoned pros. It isn't the best solution but many simply do it and move on.

Competition guys often will use flight modes which are switched on or off at specific times in their schedule (spins or snaps for example), where the models have specific
set-ups entered which allow ease during those maneuvers (much more elevator or throtthe to rudder mix for example). We don't want to fly this way all the time, only for specific maneuvers.

Are you absolutely certain the model has no dihedral??? Zero dihedral for a tapered wing means that the wing's center is flat....that is, if you cut the wing in half across its area, the projected surface is flat. In order to have that, the top of the wing droops a bit and the bottom has slight dihedral. I suspect that the top of your wing is flat but the bottom has dihedral which results is a couple degrees dihedral overall. Remove some of that and try again.

Or not....I am giving you THE answer. It's your choice whether to use it or not

MattK