Popup is too small - how can I fix that?

Ok, so I gave PopUp Pro a try. I did not change any sizes of the popup, I only changed colours and fonts. And the previewed PopUp looks fine, only the one I finally see on my page is too small (the Call-To-Action-Button is only shown half). Which is why I deactivated it (so you may want to activate it after accessing my backend - Support Access will be granted immediately after posting).
Any help with fixing it?