noobie question - rear brake issue - help please!!

I'm totally new to this dirt thing, but am very excited to get going with it. I picked up all the necessary gear, and just bought a crf250x today to start on.

I took it out this afternoon to a local park, and ran into a big issue.

When on the bike, the rear brake pedal is set up so that I can't have my foot on the peg without depressing the pedal a bit. I didn't realize this at first, and then it melted off the white plastic rotor protector. It must have gotten so hot from the friction, that the radiant heat just melted it right off.
Anyway, I adjusted the lever down as much as the screw allows, but it still isn't low enough.

Any suggestions? Is my foot position on the pegs wrong? I tried moving my foot around, but If I wanted to cover the brake I had to keep my leg elevated to avoid putting pressure on it. I was told my heel should be right behind the peg. :ugg:

.

Thanks for the advice guys.
I took Danny Walkers American Supercamp, and they were telling us to sit up on the seat, and I'm pretty sure they wanted us to cover the rear brake, which is why I was having such a hard time. As well, I'm a regular trackday rider, and don't even think about using my rear brake when out there - so riding on my toes(balls) is natural. Next time I go out I'll try standing a bit, as well as using the balls of my feet. I'll order that book today!