Mobile Site Theme not working

[ Moderator note: moved to Fixing WordPress. ]

I changed the theme on my site recently, from Business Elite to Septera. Now the mobile site isn’t loading my new theme. When in the customize portal, if I click on the icon to view the mobile layout it looks fine, but when I try to open the site on my iPhone iOS 10.3.2 (after clearing the cache), the site doesn’t look how it’s supposed to. If I click the ‘view full site’ link at the bottom, it looks fine.

I’m a complete novice at this, so my abilities to fix this are limited.

www.smooshymooshy.com