The joints will still move a bit until the glue set. With the pieces cut square, you should be pretty close to square once you tighten the screws. You cna usually move things 1/4 to 1/2" until the glue sets.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.