It does seem like a lot of difference to me . I wouldn't think any kona cotton would have any difference in front side and back side. I kown a lot of fabrice are not printed so the dyes are the same front and back, but usually there is enough difference that you would know right away if you were piecing them wrong.
I would take it apart and resew, buy maybe first just to get that top edge down next to the other on and see if there really is that much difference.