Hi,
Maybe Ive misunderstood the problem but it seems to me there is a real easy way to do what you want.
1) From your wordpress dashboard >pages>all pages
2) >Edit the page in question
3) See box “Page Attributes”? if not see screen options at the top and make sure page attributes is selected so you can see the options.
4) In page attributes >Template >Full-Width Page
Also on the same edit page you can select how the page or any part of it will be justified by using the symbol above the text box.
Hope that helps
