Hi there,
a few things to unpick here:
1. the Content Container has been set to Full Width on that page:
https://docs.generatepress.com/article/content-container/
Change that to Contained, this will respect the themes container width set in the customizer but remove the theme padding.
2. Select the parent Container Block on that page:
2.1 In the block toolbar uncheck the align wide option.
2.2 remove the % padding, and just add a fixed pixel padding for left and top as you require.
That should get you closer to where you need, let me know.