Whats Wrong?
I can’t edit it.
The RectTransform Properties of the canvas are controlled by the canvas component.
You can’t edit it and there is no need to do so.
If you what you canvas to be in 3D space you should pick another Render Mode on the Canvas Component.
But, on the vídeo tutorial Roll a Ball, the canvas has different width and height by default, and I did exactly as shown in the video, simply go to the menu and add a UI> Text but my looks like in the video is correct.
So, thanks for the help guy.
The size of you canvas depends on your Screen size / size of your game view.