Hi Jim! Thanks so much for the screengrab - very helpful to get those details!
I took a look at the template in your account. It looks like the original template design that is called "ROI University" has 2 columns. So, when you are copying a mailing as shown in your screengrab, Emma is looking back at the *original* template to make a copy with your content.
If you want to preserve the single column layout, you could setup that layout and choose "Save as Template," and that would give you a blank working version with one column. From there, you could start from that blank single column layout each time you started a new mailing.
Alternatively, our teams would be happy to update the template for you with one column. I notice the version you are using is not mobile optimized, so another benefit of a fresh design would be mobile optimization!