When you cobble together two very different parts like a wing and fuselage, it helps to check where the new CG should be placed. The formulas that have served the airiplane design world for ages do that and do it easily. Just make some measurements and plug them into this simple application:
http://www.geistware.com/rcmodeling/cg_super_calc.htm

You can do the measurements with a yardstick. Easy to do. Only 9 measurements.

Then plug in 20% for the "Desired Static Margin" and click the button. You can then read out where the CG would be for the forward location. Plug in 15% and click and you find out where it probably will fly best. Plug in 10% and you've got how far back the CG can be to give you very effective elevator control.

This application works great for situations like yours. Works good for all the rest.