Hi there,
looks like the Page Builder Container is set to Full Width.
And that probably came from the Site you imported.
Two Options
Option 1 – disable the full width layout
Go to Appearance > Elements and look for a Layout Element:
https://docs.generatepress.com/article/layout-element-overview/
Edit the element and go to Display Rules tab – where it says Location: Pages > All Pages. Change this to just the pages you want it applied to eg. Front Page
OR
Option 2 – Use the Container Block
If your wanting to create full width sections on that page – then keep the layout as is and start building your page with the Container Block
https://docs.generateblocks.com/article/container-overview/
This will allow you to contain the content but you can add background colors and images that fill the width of the screen.