Hey I bought this because I liked the option to press a back button while in the shop menu. It is there in the demo, but when I put the plugin into my project it's not there. What am I supposed to do to add it?

You mean the back button on the top right of the image? That one is a default RPG Maker feature. You should see it by default. If you don't, it's likely you had some plugin that turned off touch UI.