Issues with Hustle on mobile

On my site, hardcheapknock.com, I have Hustle installed and I'm using the Opt-in option. On the iPhone 5S (first attached photo), the user cannot see the close button for the pop-up. On the iPhone 6 (second attached photo), the (x) is off the screen and barely visible. You cannot click it to close the pop-up, which encourages the clicking of the "never see this again" option.