Three more golden stars waiting for you right here in world E level 1
Wait until the pig is at the position it is in the picture above. Also it needs to be moving towards the right. Fire the pig in an angle marked out in the screenshot. The bird will take out enough of the obstacles and the UFO in witch the pig is traveling. The pig in the bubble will continue and crash into the wall. And you will have racked up enough points for another three golden stars.
A video walkthrough of the whole thing to be seen below :