This is a very well known issue that is caused by insufficient adhesion. The corners curl up during printing.
You should increase the adhesion by:
Some people used tape on the build plate for adhesion, but I'm not a fan of tape. Not all tapes work. Tape needs to be applied correctly, prepared (sanded), etc. This is much more cumbersome than applying a little spray over the build plate. It can be successfully used on PEI, Buildtak (clones), glass and on the bare aluminium bed.