I think that's common when they are new to an enclosure or young. I would suggest beefing up the foliage in the cage so he has some places to hide. He'll probably sleep someplace he feels "hidden".
my cham used to do that when he was young too...
You could maybe attach the vines to the sides instead of having them at the top?
I cant see the whole terrarium, but it also seems that it would be better if you fill it with more foliage/ plants...