If its new I would speak to ND. After all you did buy a Dry-suit, not a damp-suit!
This might sounds rude but are you particularily scrawny or sinewy? I have heard that neoprene seals always have difficulty moulding to very sinewy people and will leak a little then.
Again, forgive me if this is a stupid question but you did have your neck seal turned in didn't you?
Hope you get it sorted, I hate that feeling when you try out something new expecting the world and it turns out to be a nightmare.
Lou