And exactly? Sorry, you are not telling us anything here. What square? What version of AE? What system? Comp settings? What else? You need to explain a lot better.
If your composition is set to non square pixels then perfect squares will look like a rectangle unless you turn on Pixel Aspect Ratio correction in the comp viewer. It's the first icon right of the view pull down at the bottom of the comp window. The solution would be to change your comp settings to the square pixel equivalent for your frame size.
To confirm this try drawing a rectangular shape layer by holding down the shift key while dragging out the shape, then when it's done, select the layer in the timeline and press the U key twice to look at the dimensions of the rectangle. They should be the same. If they are the same and the shape does not look square then toggle Pixel aspect ration correction.