all 8 worlds. but apparently that doesn't get me another star on the save file? hrm.
(needed to go to the blue place in world 1? no, that uses my coins but I still have only two stars...)
Okay, that's weird. I got the second star for beating every world, but I hadn't yet gone through all the cannons. So when I got all the coins, I didn't get a star at all, but when I went through all the cannons, suddenly I gained the third star.