I wouldn't worry too much about it , if that's the actually piece in the photo that's in question.

You build with that piecce flat and pin or tac your building surface anyways.
have the fire wall hang beyound the table slightly

The sides and the formers will keep it nice and boxie. just glue it striagth and use a triangle to check it.

My dinning room table is made of glass. it's flat, flat. however my gf don't like me build where we eat.lol

GP are pretty good about sending replacment parts if you're really consern about it.