Cantflyyet - If there are some instructions that came with your plane, they will hopefully tell you where the CG of your plane should be. If not, well the CG should be approximately 1/3 of the way back from the leading edge of your wing. Pick up the plane and try to balance it on your fingertips about 1/3 of the way from the leading edge to the trailing edge (front to back). It should balance level or slightly nose-down.

Actually, most of the small electric ARF airplanes that come with all the accessories (batteries, charger, transmitter, etc.) that you can buy these days are already balanced correctly (assuming you haven't modified it a lot). Or they will have you balance it as part of the assembly instructions. I would be surprised if that turns out to be your problem.