On this type of plane the CG is probably right on the spar. Can you feel or see the spar running parallel to the wing leading edge about 1/3 of the way back from the leading edge? If you can not detect the spar, then assume 1/4 or 1/3 back from the leading edge. in other words if the chord of the wing is 12 inches, measure back 3 or 4 inches. Slightly nose heavy is better than tail heavy for first flights