A heavy wing panel is more pronounced in a high-g maneuver compared to level flight. 1/4 inch seems like a lot.

Try this. Put your plane on a table and stand about 10 feet out in front, looking at the nose. Gradually kneel down until you are looking at the leading edge and just across the top of the wing. you can easily tell if one trailing edge is higher than the other.

Measure both sides from the fuselage out to make sure they are the same. If one side is only slightly longer, you can boost it out with a soft balsa "rib." You should weight the other tip to balance.

I've had a couple of 4* 60's and one thing about all of Sig's Stars I do not like is the type of wing construction. They use a multi-spar type construction rather than a sheeted leading edge. This type construction is easier to warp than the D-tube, sheeted type.

I have stiffened these type wings with a couple of extra stringers. I used a 1/8 square spruce spar, mounted from the main spar at the center sheeting diagonally back to the trailing edge on top and the opposite diagonal on the bottom (center sheeting at trailing edge to the main spar at the tip). Looking through the wing they make an "X." This stiffens the wing in twist.