If the CG was too far back, the elevator would be very touchy, if it was too far forward, not twitchy at all. Sounds like either a wing incidence problem, thrust angle problem or elevator incidence problem, if I were to guess without seeing the plane. If the elevator is very sensitive, you could try easing the CG forward a bit. You can try shimming the trailing edge of the wing where it bolts to the plane to decrease the incidence a bit and see if that helps. Do a search on CG, and Incidence in these forums as there is a ton of stuff on both these issues. Good luck!