Yes, I figured it out —
The Page Attributes box only applies to additional pages that I’ve made (i.e. “About” pages, “Bio” etc.), but not the actual MAIN blog page.
After taking a closer look at the code for the one column page php file, I saw a css class tag called “onecolumn” – so in the main div container for the main blog page, I added this attribute. It worked like a charm!
Thank you for your help!