Use the arrow keys to move and space to flip. If you get stuck, try jumping and flipping at the same time until you get out. You will lose if you hit a baseball, but you can go through baseballs during a flip (you have to wait 4 seconds between flips though).
Karim (my helper during a previous week of camp) showed my how to trick Sratch into making a super huge sprite, like we did with the platforms here.