can't download app

[seamster]

I have heard good things about this game so I thought I would give it a try. I downloaded it from the itunes store and it has appeared in my itunes library, but it will not download to my phone. I sync my device and the rest of my apps work ok, but Kingdom rush just sits there. anything I can do? Any help will be gratefully received, otherwise Im just going to have to ask for my money back

Thanks

seamster