Changing template without changes showing up

Site URL: https://zoehough.com/

Hey,

I want to change template from Henson to York.

I followed these instructions about editing in preview mode https://support.squarespace.com/hc/en-us/articles/205815598-Switching-templates

"To start editing your site in Preview Mode, in the Home Menu, click Pages. Remove the demo content and move your pages from the Not Linked section to the other navigation areas. Visitors won't see these changes until you publish the template."

I did this, and started editing. I checked my site (in another browser window) and changes had indeed showed up in my henson-template designed site... the main sentence was now as per the york template, and all the images in the 'banner' for each of my projects had disappeared so I had to re-upload them.

Is there another step to take to ensure that no changes occur to my original design while editing in what is meant to be 'preview' mode?

I simply want to edit my site in the York template preview-mode, without affecting the content in the original Henson template.

Possible?

Thanks for any tips!