Adjusting spacing in clustered column chart

Hey everybody,

I tried searching and couldn't come up with anything. How do you adjust the spacing between clusters in a clustered column bar graph? I've attached an image of what I want the final graph to look like, and how I've got it so far. The spacing that Excel generates for my graph (on the left) is far too wide and looks a bit weird. The graph on the right was made in Adobe Illustrator, but I'd like to generate it completely from Excel without any touch ups.

Thanks for the help!