Hatch Problem

So we started on the hatch. We traced the profile for the ribs, cut it out on thin board, matched it up. Determined the width and measured out. The ribs are cut out of 3/4" birch, matched to the profile again and pieced together and before attaching and building the frame, we did a dry fit, checked the measurements and it was time to put together.
After everything was set up and put together and checked the fit - for some reasons, the fit was off, made some adjustments and achieved a better fit. We have since put on the outer and inner skin, checked measurements again and turns out we are out of square by about 1/2" - 3/4". Measurement from top to bottom matches, but we're off corner to corner. Short of taking everything apart and starting over - what are the options??? I know builds aren't perfect, but this is driving us nuts...
After everything was set up and put together and checked the fit - for some reasons, the fit was off, made some adjustments and achieved a better fit. We have since put on the outer and inner skin, checked measurements again and turns out we are out of square by about 1/2" - 3/4". Measurement from top to bottom matches, but we're off corner to corner. Short of taking everything apart and starting over - what are the options??? I know builds aren't perfect, but this is driving us nuts...