A lot of that slack should pull out when you pull it tight to apply it. Cub wingtips are hard to get right with a single piece because the covering needs to both shrink and stretch. I've done my .40 size Cub in both ultracote and solartex. With both, I put the heat gun to it, blowing the heat from the tip into the wing so that it would heat up the whole wingtip area. I then pulled the covering hard right at the spot where the heat was coming from, which made it stretch to pull those side wrinkles out. I did that at probably 10 spots all around the wingtip with each spot stretching the wrinkles out that the previous spot had caused. If you are using stixit to apply the koverall, the same process should work for you. Of course, since you're using koverall and can hide your seams with filler, it won't hurt anything to cut the fabric where that big wrinkle on the side is and fill the little seam that the overlap makes with dope. No one will ever know it's there if you do it right.