You can easily add styling to any button shown in the popup. We have selectors for each image to work best with the configuration you've chosen and your site's overall looks. So, for instance, you should be able to add:
.sclogin-social-login {width:500px}
You can target each individual button to add clears or move things however you want like:
.sclogin-social-login .social-login.facebook { clear:both; }
Finally, the SCLogin module also lets you select your own custom images, which may work better for a more narrow view.
I hope that helps,
Alex