Before you take it to the bandsaw again. Sand the outside and keep it at 90 degree messured from the bottom that is 90 degrees from the inside... Right!? When working in the bandsaw, check that it saws in 90 deg (adjust the baseboard of the saw). Pay attention to making the bandsaw cut as close as possible to he line and be smooth. The outside back-support wont need any sanding - it will support the ply good anyways...
