Don't look a gift horse in the mouth. List something for sale QUICK ! ! !
You say you are working from a semi kit. The fellow that did the CAD to make up the cut file for the kit might have messed up and used 1/4 square instead of the 1/4x1/2
What you could do is what some of us suggested in your other thread asking about an oddball size stick of balsa which you led us to believe was for the spar. Namely go with the 1/4 sq but use good aircraft spruce or at least good tight and straight grain bass. Or if you can find some tight growth ring count southern pine I understand that it is a strong yet supple wood too. Then just be sure to add the vertical webbing between the upper and lower pieces to lock them together to form a box spar.