Ken;
This is not totally uncommon to make a mistake of this sort. What you did is in your trial fitting of the parts you inadvertently left out checking inner trailing edge to Tail post measurement prior to final gluing your wing tube in place.

As the Fuse Sides are identical this is the only place this mistake could be made is in the wing.

To fix the problem you need to check your measurements. Check the trailing edge to Tail post(Or end of the fuse)(If the fuse is crooked this isn't going to work either) make sure that these distances are the same. Now check the Stab to the wing and insure these are the same as well. If and only if these are perfect then you can use a 1/8 piece of Light ply laminated over the root of the wing and sand flush to fit the fuse. Cover that small area check your measurements again. If they are all good as well as the incidence, CG Balance and Lateral balance your ready to test fly.

The other place that you may have made a mistake is the Tube alignment reinforcements inside the fuse. as the glue was setting it may have shifted. Thus moving the Tube slightly forward causing the gap to appear from the leading edge to the trailing edge.
Repairing this problem would be to either ream the whole larger an make another Ply reinforcement. Removing the Old one and replacing it with a new one. Or removing the bottom wing covering in the middle and readjusting all the Tube alignment holes in each rib.