"Two page" site setup (One Page + blog page)

Hi,
I would like to set up my one page site with a separated blog.
What I mean: I have a standard one page site with a header main menu, where every menu item is linked to a one page section, except the ‘Blog’. This is linked to a second page which is a full width masonry blog with the same header and footer layout as the ‘one page’ page.

I added the full width masonry blog page as a new menu item under appearance/menu and checked also ‘Main menu’ theme location check box.
What is happening now: the ‘one page’ page is working. The header menu is also working it is jumping to the right sections, and if I click ‘Blog’, it is jumping to the full width masonry blog page. It’s OK so far. But when I want to use the main menu on the full width masonry blog page, it’s not working because it is looking for the one page sections on the full width masonry blog page.

What could be the solution here?

Thanks,
John