When i float my list in a widget it breaks the widget

Hi – I want to make the list included in a widget on a site that i am working on (see here: http://heattreatforum.flyten.net/) three columns. It’s the “Latest Forum Activity” widget. When I try to float the list to the left it breaks the widget (or at least the border). My plan was to float the list to the left and then reduce the width, forcing it into three columns.

Is there a better way to do this that doesn’t include float? Or what am I doing wrong with the execution maybe?

Thanks!