That's a lot of extension on the bike rack. I've hauled my scooter on the back of my pick-up on one, and I can tell you they do move around. First, I would not tie-down on the handle bars. On most Chinese scooters, or any scooter of that size, the handle bars are held-on with one bolt, which works loose when you put too much strain on it. (Ask me how I know this) I would anchor the scooter to the top of the front shock mounts, and/or at least wrap the tie-down around the steering column below the handle bars. I use 3-4 straps on each side and they still loosen-up, so I would be sure to check them pretty often. I'd anchor to the shock mounts on the rear also, assuming you have two rear shocks, which some don't.
Good luck, good travels, and nice scoot.
Oh, and I'd get a longer loading ramp if you can. Your center stand will likely catch on the ramp when you try to load and unload, and can be a real pain, and you might damage your scoot. If I use mine again, I'd get one as long as the rack itself. Mine caught on the rack and I ended-up dropping the scoot.
