Your Narrative Publish post will fill the complete space that it is given from your website. If your website does not have a defined max width then your Narrative post will essentially fill the full width of your browser.
Alternatively, if you website has restricted the blog with to a small width then your Narrative post will appear very small.
How to change the width of your blog:
The following steps will allow you to define a pixel width for all your blog posts.
From the Home menu select 'Pages'
Open the blog that you would like to make the changes to
Select the 'Blog settings' at the top of the page
Select the 'Advance' tab
Paste the following under the 'Page Header Code injection' text box
6. Press Save
7. Reload your post
Note: You can also adjust the blog width to your desired width by changing the 'max-width' pixel amount. We suggest anything between 700-1500px. Though please note, this method has not been extensively tested on all Squarespace themes.