Hey there, Mandy!
Ah. I see, now!
In order to correct this, you'll want to add some padding to the mc_signup_form id. So, we'll add something like this to the Style.css file:
My choices of 250px and 50px are totally arbitrary, but give you something that look like this:
Screenshot -- http://cl.ly/1I1Q0e2D2B3R271p1h3s
And since we're changing the height of the form, we'll also want to change the height of the plugin area so it adjusts automatically. Something like this should do the trick:
Generally, I just play around with Chrome's Developer Tools so that things re-render on-the-fly to give me an idea of how things are going to look on the page. :)