Q: How do I get a full screen pre-view on my ipad air when connecting my samsung NX 300 camera

Try this  - Reset the iPad by holding down on the Sleep and Home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider - let go of the buttons. (This is equivalent to rebooting your computer.) No data/files will be erased. http://support.apple.com/kb/ht1430

Doesn't solve your wifi connection problem, but you can use Apple's camera connection kit to transfer pics/videos from your camera. You can connect the camera to the iPad using a USB cable or use the camera's SD card.

Using The iPad Camera Connection Kit

http://support.apple.com/kb/HT4101

 Cheers, Tom

http://www.samsung.com/global/microsite/SMARTCAMERA/howtouse.html

That would be a question for the App developer. Whether or not they have a full screen option in the App.