iPod 5, it won't download the app

So the other day, I wanted to download an app (Ask.fm) and I went to the App Store and downloaded it as usual. After I waited 2 hours, I checked on it again, and there was only a sliver left. It has been 2 weeks and it won't completely download. If I look at the app store, it says it is already completed and I can open it. I tried opening it, but obviously it didn't work. I tried to delete it, but it didnt work.

someone please tell me a solution to the problem. Thanks