Hi there,
that space comes from the Separating Space in the Customizer > Layout > Container.
If you’re wanting to create full width pages where you can control every aspect of spacing then i would suggest:
1. Set the Content Container to Full Width
This will give you a 100% full width page with no Theme Padding or Separating Space.
https://docs.generatepress.com/article/content-container/
2. Build your Page with GB Container Blocks where you can set the Padding and margins you require