First of all don't feel too bad. Many pilots don't seem to know what their feet are for. This is especially evidenced when transitioning to a tail wheel or seaplane. Yes there are exercises. Some serve to teach initial rudder skills and others do better with honing existing skills. Another good tool to learn rudder skills is a yaw string. They don't work well on "tractor" singles though... They are commonly used on sailplanes/gliders. I might recommend purchasing an instructional flight in a glider. Inform the instructor of your rudder situation... would likely be money well spent.