That's a huge CG change. Are you sure about that measurement? It's pretty rare for a Cub to need significant nose weight assuming you're running an appropriate engine. I'd double check that measurement and go ahead and pull up a CG calculator to make sure you have the location right.

What method did you use to do the measurement? The right way is with a square of some kind that you can butt up against the leading edge and know that you're getting a precise reading at the trailing edge. If you'll give me the overall length of the plane and the wing measurements, I'll compare it to my Cub which flies nicely.