In order for the AR kit in your device to display your Avatar, it needs to scan the flat surfaces around the room you are in. This is how it determines where it can place the avatar on your screen.
If it keeps scanning, try walking around your room slowly letting the camera scan all of the flat surfaces at a distance.
Make sure that there is plenty of light in the room. If it is too dark, the scan may not work and it will continue to try and scan for well lit surfaces.
Please note that surface scanning may take several minutes!