plastic pieces break very easily

Tried to adjust, then the plastic pieces broke

The breakaway end of the lengthwise metal strip you have to cut away isn't even like the other end, so doesn't want to insert into the plastic corner piece as smoothly; the plastic pieces also break easily, which doesn't help when trying to get the rough edge of the metal strip to slide in.

Plastic pieces don't fit the metal rails

The thing fell apart and broke at the corners as we were following the instructions step by step