Hi Helsingborg,
The calendar looks fine, it’s your theme that’s the problem. You’re going to need to set the template to be full width somehow in your theme. This is usually accomplished with a combination of PHP and CSS to conditionally set the layout for a specific page (in this case the calendar page) and then set the CSS so that everything looks good. There are a number of threads in the forum dealing with this issue. Try searching around to see what you can find. There are also the template options in Settings > The Events Calendar > Template that may help.
We do our best but cannot guarantee complete compatibility with all the themes out there but it’s impossible to achieve 100% compatibility.
Good luck!