I mean you can do what you did there, screenshot the layout. You could then crop it to the layout area and scale it to what you have as the layout size in the image editor.
An event way to possibly do it to set the canvas size to be the same as the layout size and use the snapshot canvas action to get an image. There may be some finickiness to deal with such as waiting a tick for things to update before snapshotting. You may also need to turn off full screen scaling. There may be other issues but i'm not sure. I've had issues in the past of capturing everything that way.
Another way to snapshot the canvas one screen at a time, and then piece them together later.
Either way you may end up with a rather large image which will be slower to download and take up more vram. It doesn't mean you can't do it but generally most games have reusable images that they place all over the level for decorations.