Are you sure that setting has anything to do with it? As of right now, I’m not seeing anything telling the theme to display your content in the full width template. The Page Builder Container (https://docs.generatepress.com/article/page-builder-container/) is set to default, and none of the Layout Elements have Display Rules.
Edit – thanks for the video! Just looks like a bug in the Customizer itself, I’ll take a look. The live page shouldn’t experience the same issue 🙂