Hi and welcome Anne:
As I understand it this issue happens in video mode. Most likely you have changed the video image format from its default to a different proportion. See P53 of your manual to change this. If you don't have the manual (it should be your first port of call for any issues) you can download a copy of one as a PDF HERE
cheers, TREVOR
Before you ask us, have you looked in the manual or on the Canon Support Site?
"All the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
