Finally Finished New Super Mario Bros...

For 2 months playing, I finally finished the New Super Mario Bros game on NDS, and got 2 stars. First star is for beating the big boss, Bowser(?), and second star is for collecting all gold coins. However, there are 3 stars, but the last star is for finding out all stages. Give me a break! 2 stars are enough!
Here is the walkthrough for this game: Guides: New Super Mario Bros. Guide (Nintendo DS), New Super Mario Bros. Walkthrough