I've only worn mine a couple of times and not for very long, but I haven't noticed any stretching. I know that's not the answer you were hoping for, but maybe other girls can tell you differently
I didnt size up either and they fit snug and really hurt at first but i did notice they were a little more comfy after a few hours of walking. I wanted them to work so bad.
It just depends how small they are on you. I also make a point of wearing them at home a lot to break them in some more. silly, i know!