Sides on cube don't work

This has been bugging me for awhile... I know I must be doing something wrong- maybe you'll be able to find what I'm doing wrong.

I'm trying to make a basic cube. I make a 100x100 square (linear) by setting the coordinates at (50,50), (50,-50), and so on.
I then make a total of 6 of these, and using the Properties tab of the Inspector, I maneuver them into position.
If I remember my high school geometry correctly, it should work fine. And it does, at least for the top, front, back, and bottom. But the left and right sides of the cube are somehow not the same size... Here's a picture so you can see what I mean. (I've rotated it, so the light blue would be the right side. The yellow is the front panel.) If I adjust the X-scale for the sides to 110% it looks fine.



Here's my file, feel free to play around with it to see if you can find what I'm doing wrong. Thanks!

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It's because your project is set for DV, which has non-square pixels.

Yup. That's it. Thanks!
So how would I make a cube in DV? Just scale it differently?