Issue with Changing layout using Fluid Engine

Hi, 

I have recently joined SquareSpace and I really loved the design of my website for desktop that I made. It is now a public site, however I have attempted to change a few issues with placement, re-sizing of images and such for mobile version. In some cases the spaces between images can be changed without the mobile version affecting the desktop version. Unfortunately, when it comes to re-sizing images or editing content blocks to best fit the mobile version, it completely messes up my desktop layout. 

I am unsure how to re-size images and blocks without it affecting my desktop website. It's a little frustrating as I cannot see any actions which would allow me to pause or freeze certain elements in pace, in order to prevent editing and manipulation on another version of my site. I have provided screenshots of both my desktop and mobile versions, here you can see what I mean. I do hope that there is a solution to this as I would eventually like to have a 'shop' and for things to run smoothly...

Thanks and hope to hear from someone soon.  

You can see this 

https://support.squarespace.com/hc/en-us/articles/6421525446541-Editing-your-site-with-Fluid-Engine#toc-mobile-layout