Hi Yvonne,
I took a look through your site and I see the issue on my end also. It looks like there may be a conflict with the theme or maybe an error with some custom CSS.
I found this line of CSS in what looks like to be a customs css file:
#event-categories { width: 350% !important; }
Heres a screenshot of where I found it in the inspector: http://d.pr/i/Tfjr
If this is a custom css file you should just be able to get rid of that line and the plugins CSS should be able format that for you correctly.
Hope that helps
Neill