pop-up not resizing for mobile

I have pop-up! installed on my site and it works well EXCEPT...

It doesn't seem to resize for mobile devices, so visitors can't get past the pop-up (there is no visible X...all they can do is click the pop-up image which redirects them elsewhere)

How can I get the pop-up to be completely responsive?

See it in action here: http://makeyourbodywork.com/