This can actually be a difficult quilt for the very reason you mention. Could you post a photo?
If the strips aren't too wonky, I would start by starching and blocking the strips into submission. (Sharon Schamber has some good videos on Youtube about how she stretches and shrinks wonky blocks to fit.) If they are still wonky after starching, I would look for a few places where I could separate and re-sew to "adjust" the strips. Worst case, I would look for a way to cut off any excessive wonkiness. *Only* after a lot of starching, though, to stabilize as much as possible!
Have you already cut the sashing strips? Next time I would *heavily* starch the fabric before cutting the sashing strips. This helps keep them from getting wonky too.
A book I have recommends not cutting the sashing strips at first. It recommends cutting a straight edge on your sashing fabric, then sewing your stacked coins strip to it before cutting the sashing fabric to size. They say this helps control the wonkiness. (Personally, I think heavy starching would help more.)
Very worst case, I would cut down the strips and make several crib quilts.