no euclidean "perfect" shape can ever be produced in the real world. Heisenberg's uncertainty principle precludes it, because we can never know exactly the length of anything at scales below the plank constant.
Unless you are using really precise tools it will be nearly impossible for it to be PERFECTLY square. Also, if it is a box shouldn't it be a cube? You can always try to use a computer to print out a template and trace it.
