Reshaping photos in Themes ps express

[defaulty420nhvep9rd]

This is driving me crazy. I used Themes (actually Thanksgiving theme) to create an ad. 
The theme has two circles for photos. One of my photos would not fit within the circle and whilst moving the circle around and trying to size the photo to fit I somehow manage to reshape the circle to more of an ellipse shape.

my photo then fitted perfectly. 
However, I have tried to do this again and I cannot fugure out how I changed the circle to an ellipse. Can anyone help please ? Attached photo shows shape I ended up with (which was originally a circle )