We can address the stretching later. For now, try choosing an image that is a horizontal rectangle.
I use photos that I take of the actual light.
You can store both on and off in a single button. The entry of the second link is a little awkward (and will be fixed). After the first link, go to the next line (where it says Data) and type the second. Then save. Your button will send on, off, on, off when you press it.