ThunderTim35 answered your question about points & bubbles, but I wanted to mention something, JIK. You do not have to get those "2 more stars" from the current island. You can go back and play earlier levels if you want, to build up stars. As mentioned, you can get higher points/more stars by trying to complete levels with lots of consequetive pops & drop bonuses, as well as using the fewest bubbles...