If its the same as the 250 2C then yes, that is the filling hole but it takes aaaaages. I had the same trouble with the 70cc (lol) I was supposed to fill. You could try pumping the forks, ever so gently. That's what I did and it speeded things up slightly. I had the forks out of the bike though. Good luck with it.
Just a thought, maybe loosening the drain screws at the bottom of each fork leg might let air out (until the oil starts to come out)?