Is the ankle strap already at it's max adjustment? It seems like you're only engaging about 5 teeth which probably won't be enough on the hill. I'd try to get that strap centred on both sides of the boot if possible.
Yeah you don't really want to toe or heel of the baseplate/gas pedal hanging over the edge.
Wiredsport has a good writeup somewhere of binding adjustment. Basically you want to strap in a laced up boot, then get the board on each edge and check the angle it'll reach before the toe or heel hits. Make adjustments until those angles are as close to equal as possible.