You've resized the layer, not the whole image/canvas. You could now go to the Image menu - 'Fit canvas to layers'.
What I prefer to do when resizing a final image like that though, is just use the Image menu in the first place, select 'Scale Image', which does it all at once.
What I prefer to do when resizing a final image like that though, is just use the Image menu in the first place, select 'Scale Image', which does it all at once.