Nifty Fifty

Not one to procrastinate, I ordered a nifty fifty lens yesterday which arrived today and so I made the most of the 3 minutes I had with a willing subject to start experimenting.  (After that I had to make do with the dog and her nose - see extra).  I'm pleased so far and excited to start understanding settings.

One puzzle though, my photos have changed shape to be narrower than they were 3 days ago here.  Everyone has had a play with the new camera and the settings have obviously been changed...but where?  It's not a disaster, but I'd like to know how to change it back...