As I said, I'm on the new editor. We cannot use apps nor can we add code to items.

I'm not familiar with "thin content" @MileandaThird Can you please clarify? 

Moz description "Your page is considered to have "thin content" if it has less than 50 words (excluding navigation and ads)".

So my homepage was the standard "header", "main banner", "location and hours" and "Footer".

This was deemed to be less than 50 words.

Thanks for explaining that. I think you are write about adding more content. For the canonical tag information that @whitemonkey linked might be able to be added under Website>Integrations, but I don't know how specific you can get since this section is a blanket area for the entire site and not specific pages. Would the Embed Code option work? It wouldn't be in the header but in the body of the site.

With all due respect, if you are "not familiar with Square nor the new editor", why do you keep responding to my questions about the new editor?

Some suggestions to solve that with the older editor can also apply to the newer website editor. For example, a canonical tag is added a similar way by adding the code for one in Website > Integrations > Add Header Code. As for an H1 tag, you could add one with the Embed Code section to individual pages, although you'll have to write the code itself.