Display Arrangement Missing

I'm trying to set up my iPad 2 as a second monitor to my MacBook Pro (with air display). Initially, it worked out fine but after trying it again, the display not only doubled the image on from my Pro, but also shank the Pro's resolution to iPad size. In order to fix this issue I need to go into System Pref> Display> then Arrangement, but this option for Arrangement is not present. Could someone help me render this issue?