That looks much less bad than my first balsa build I ever did for sure.
I believe the Skylark kit, like the eaglet, has little supports that fit in the holes in the fuselage sides. They go next to the supports for the fuselage stringers that are placed about at the midpoint of each hole. Here's a really early photo of my eaglet with one of the pieces installed in the rear hole:
I'm pretty sure they don't really do much of anything structurally, they're just there to help the covering look nicer.