Slide-in not showing 'close' option on mobile

I have installed the Slide-in plugin and it's working well BUT when it happens on my iPhone (and I've had a few comments about this), there is no option to close and the box fills the whole screen, so the person visiting has no option but to close the window and not read on. As I get a lot of mobile traffic I believe this is actually a detrimental quality and I will have to remove it if I can't find a fix.

Any ideas how I can either A) not have it pop up at all on mobile devises or B) Have it so that it is smaller and the close button is clearly accessible?

Many thanks

p.s. the website is