Object changes proportions as I rotate it

I've encountered a really weird issue with After Effects, rotating an object will make it drastically change proportions (as shown in this gif) the comp size is 1000x1000 pixels and the circle is 868x868 pixels



This stemmed from another issue where holding shift would lock the proportions to an equally weird size instead of locking it where it is. (I overcame this by just fitting it to the comp size and adjusting the scale property)

Thank you in advance :)

Woah! thank you so much! It was set to "HDV 1080/DVCPRO HD 720 (1.33)", I set it to square pixels and it fixed it instantly, thanks again.