Why is Fan module extending beyond it's borders

It's a responsive issue. It looks like if you add the following to your template, it will make the Like Box dynamically resize:We're working hard to implement fixes for each of the FB social modules that doesn't natively support responsive templates. This fix will *not* be in the upcoming v5.1.0 release, but should be in a release shortly thereafter when we can thoroughly test it more.

Thanks,
Alex

Peter,
We'd likely include this in the v5.1.1 release, whenever that release is due. That would be a 'rollup' release of any issues found by users in the upcoming v5.1.0 release or minor improvements like these.

To add now, that line should go in your template's CSS file. It looks like the below file is likely the one you want:
/templates/refresh/css/template.css

I hope that helps,
Alex