Hi Victoria,
I believe you’re using 2 Layout elements for blog page and single posts.
You blog page seems to have a Layout element container setting of “Container Area: default” while your single post is set to Full-Width but has a Content Width of 800px which causes it be more narrow.
To fix the narrow blog page, you can simply change its Layout Element Container Area setting to Full-width and keep the Content Width blank or set it to a value higher than 1240px if you find the current width too narrow.
To fix the more narrow single post page, go to its Layout Element and set the Content Width value similar to what you’ve set on the Blog page’s layout element Content width.
Let us know if it works for you.
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