This level is shaped like a star. What you want to do is move back and forth (firing in the direction you are moving) to almost the edge of the star. Go back to near the other side and repeat. If the rotators start going out of control use your bomb.
You don't want to go all the way at the edge since a flower can spawn and kill you. Here's a video showing the madness, if you haven't played the game a lot it may look like gibberish to you.