Is the nose wheel in alignment with the rudder? What I mean is do you have the rudder trimmed so that it is lined up with the fin? If the plane does not taxi straight down the runway it is tempting to correct this with the trim tab on the transmitter. Correcting the steering this way will also change the trim of the rudder since they are controlled by the same servo. Having the rudder aligned is more critical than the nose wheel. The nose wheel should be adjusted manually.

Also look at the engine and make sure it is not canted to the right. Having the engine canted to the right 2 or 3 degrees is OK. Lots of planes need the engine canted to the right a little bit, but having it way over to the right would cause a problem like you are having.

Eric