Garry,

Start with the CG at the 3 3/4 inches back mark. Balance the airplane there with the fuel tank empty. Achieve balance by moving your battery forward or aft until the plane is balanced. Move the batter as it is the heaviest and easiest to move. Don't add weight.
Once the plane is fueled up it will be nose heavy and will move toward balanced CG as fuel is burned off. Once you have flown the airplane and get it trimmed out you can move the CG forward toward the 3 inch mark to see if the flight characteristics improve. Remember, "A nose heavy airplane flies poorly, a tail heavy airplane flies once".
Good luck.

Regards,
doubledee