That's a great question, Audrey! Before saving each component as an image, I connected the shapes/icons by duplicating them and adding them to the right until I got the width I wanted. For example, for the mountains, I found a few different icons, duplicated them, added them next to each other, and changed them to the same color. I also added a long rectangle underneath of the same color to give the mountains more of a base. To be safe, I extended the mountains and rectangle to be longer than I thought I would need. You can see all the icons/shapes I used here:
https://community.articulate.com/articles/how-i-built-this-recycling-parallax-interaction-in-storyline-360#:~:text=keep%20image%20quality.-,for%20example%2C,-I%20selected%20allI used this technique for each layered component before exporting each of them.