To force quit any app that is backgrounding:
1) Double tap your home screen
2) You should now see that your phone has zoomed out and all of your backgrounding apps should appear in one horizontal line
3) Swipe left to view additional apps that are currently being backgrounded.
4) Find the app(s) you wish to force close. Swipe up to force close them.
Please note that if you tap on the app it will open.
5) Double tap your home button to bring your device back to normal.
Click this link to read up on more information on what Backgrounding is: http://support.apple.com/kb/ht4211