Somehow i raised the green Nav grid and i couldnt work out how to reset it...how do you reset this if you accidently change it? I was flying around on free camera mode and when under the world and tried to get back (i end up having to turn off free-cam mode to do this) and then i notice the green grid was off the ground.

That is normal - the navigation lines are drawn a bit above the surface of the tiles. It's not usually noticeable when the camera is in its default position.

Ah okay, it looked like the green grid was about a foot higher than normal so this is just a visual thing.