IPod touch 4th generation zoomed in

Hi Guys,
My iPod Touch 4th generation has an annoying problem.
I was just playing games on it, and then suddenly it automatically zoomed in.
Everything became big even the icons, letters and numbers. I tried to turn on and off wondering that it will be back to normal, but same thing happened.
Does anyone know how to bring it back to normal? What should I do and what's the reason why it happened to my iPod?
Thank you.
Bryan
