Aspect ratio on my screen is wrong while in the tools it is set correctly

Hello,

In CD, I draw a square, but on my screen it looks like a rectangle.

I checked if I had lost my settings in Tools>Options>...>Zoom tool. But no. There, all is set correctly. The scale is perfectly 2cm wide and 2 cm tall.

What strange is, is that, how far I change these settings, it is never reflected on my drawing's aspect. I changed the scale in the options so that the 2cm wide scale measures 0.5cm, there is no effect on my drawing's aspect.

Any idea how I can have a square looking like a square and not a rectangle ?

Thanks,