I would suggest checking to see if you can resume the download with this procedure:
If your download was interrupted on your iPhone, iPad, or iPod touch
You can manually resume the download on your device with the following steps.
- From the Home screen, tap the iTunes icon.
- For iPhone/iPod touch, tap More > Downloads. For iPad, tap Downloads.
- Enter your account name and password.
- Click the "OK" button.
- Click the Resume, Resume All, or button to start the download.
If you cannot complete the download on your device, you can finish the download in iTunes on your computer and then sync it to your device. For instructions, see the following articles:
- iTunes Store: Where can I download and sync my purchases?
- iTunes Store: Transferring purchases from your iPhone, iPad, or iPod to a computer
From: iTunes: How to resume interrupted iTunes Store downloads
All the best,