Hi,
in Customizr > Layout > Content Width i have 74%, the max available.
Looking at my page with firebug, I see: .x-main {width: 71.536945%;} [picture 1]
If i move this to 74%, the gap between the main content and the sidebar is thinner, exactly as I want it to be. [picture 2]
Can you try testing for a plugin conflict. You can do this by deactivating all third party plugins, and seeing if the problem remains. If it’s fixed, you’ll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time.