It's not normally necessary to use rudder in a turn, as a coordinated turn isn't absolutely necessary, but, if anything, you should be applying rudder in the same direction as the turn, not opposite, to get a coordinated turn.

The wing on the outside of the turn has the aileron in the down position, that creates greater lift, hence the model rolls towards the turn, but greater lift = greater drag, so the plane tends to yaw away from the turn, which can be corrected by moving the rudder into the turn.

If you move the rudder away from the turn that's a good way to get into spin if you do it enough!

Of course, you should also be giving up elevator to make the plane 'climb' into the turn.

-David C.