decals that don't fit

I realize we should always dryfit parts and so forth, but how do you insure decals are going to fit before you get them off the backing? Case in point, I just finished the F86 Hasegawa Mig buster. Build went OK, not the best I have done but OK. I was working on decals when the yellow black checker pattern for the tail and the yellow black stripes on the wing tips simply were too big. They overlapped the other side. Unfortunately, they would not stick down over the edges for some reason. I am now faced with decals which when you look up close, clearly are too big. I am frustrated. Bottom line is, how do you dryfit these things so you can trim when necessary. Usually only happens with tail insignia and stripes on fuselage or wings.