This worked, but as noted, it has spars.  The spars also help give some joint surface to the cap strip/sheeting interface.  Also, spars help to give a hard point for bellcrank mounts.

I'm not a structure expert, but you might save the carbon until some others weigh in.  I don't think that will solve the problem.

The foam that has been cut away between the "ribs" is not a big deal.  The foam is not providing much, if anything, anyway.

You MIGHT be able to salvage the wing by adding some center sheeting.  However, by cutting out the foam closer to the center section, there does not appear to be enough left to add some center section sheeting, cut at an angle, so that in plan view, the center sheeting is a trapezoid shape, longer side at the forward end.  Right now, your center sheeting will have a stress riser right at the outer edge of the sheeting.  I do not think the carbon strip will help much.

I have built partially sheeted foam wings, covered with polyspan and dope, and they hold up.  But, only on smaller planes, such as Nobler size.  I managed to get away with it on something a bit larger (575 sq. in.) but, in the end, fully sheeted is the way to go, no matter what I build now.