You are correct, it's not the container -- the answer is actually in the .ascx for the EventMonth display itself. Look for the file EventMonth.ascx, which should be in <%webroot%>\DesktopModules\Events. Open it in any text editor, and look for the area near the middle of the file that reads:

<asp:datagrid id="DailyEvents" runat="server" Width="400px"

Replace the 400px entry with something more appropriate (in your case, try 100px), save the .ascx file and reload the page. You should notice a lot less left/right wasted whitespace. I had this same problem myself, as I am using the calendar module in an intranet setting, on the homepage, and the default width was badly disrupting the layout of the skin I was using.

I hope this helps...