I'm not sure if this is of any help, but when I had the same issue and I looked at ScrollableLayer, it seemed like I had to create a very, very large image. So I decided to use a trick instead:
background.do(Repeat(MoveBy((-500, 0), (500/SCROLLING_SPEED)) + MoveBy((500, 0), 0)))
What this does is it moves the image visibly to the left by 500 pixels in a certain amount of time (depending on the scrolling speed (set to 0-100)), and then quickly moves it back to the right by 500 pixels. This last movement isn't visible to the human eye if your image's pattern repeats every 500 pixels, but it "resets" the image position so you don't need a huge image for your level. The same image just moves left and right continuously.
I'm not saying this is better, but it is just one line of code so might help you out 😅