I've done a few ginger beers and always get a very low FG, around 1.005, that is okay because you are aiming for a low FG on ginger beer, any higher than that and you risk ginger flavoured bottle bombs. Not sure what it says on the brigalow kit but I'm pretty sure it says to wait until the FG is down around the 1.005 mark on both the Coopers and the Morgans kits.
EDIT: Whoops, should have read that a little closer... I get a low OG as well, I think my last one was just on 1.034 and that was using 2 cans of Coopers GB and a kilo of sugar into 20L, the brew came out fine.