It takes a lot of practice
I did the same thing as you, challenge AAA thinking it would be no problem, and because of that, I managed to put myself out of the running for any of the really big prizes. I eventually did beat him though.
My advice;
Make sure for the first two levels you clear completely. If you don't, just start again. It gives you a good groundwork for the rest of the levels.
I say during those first two levels, also use the cheatcode at the end of one. (destroyboulders), and that will double your score. But if you use it, make sure you've completely cleared the level, otherwise it doesn't have quite the effect it should.
After that... it's just trying to clear as much as you can. There is a certain amount of luck in there, for properly placed blocks and stuff.
Best of luck!