makariosousta I'm not sure how the back button works at all. You're not even using the project included in the plugin.
Make sure you follow the tutorial step by step, in particular Exporting the project.
ncluded in the Windows Phone Plugin for Construct 2 is a ready-exported project that we just need to drop the relevant exported files into. Never export directly from Construct 2 into this project otherwise vital files will be overwritten. I generally have two folders, one for the project and one for the exported files. Then I just copy what I need from the exported folder to the Windows Phone 8 project folder, helping to ensure nothing important gets overwritten.