Super Mario galaxy how do you get to final galaxy but it is not working

to get to bowsers galaxy reactor complete Bowser's Dark Matter Plant and Obtain 60 stars when you do this you will be asked if you want to fly to the center of the universe say yes to enter the level

To unlock Grand Finale Galaxy get all 120 stars with mario, then beat the final boss to unlock Luigi, then get all 120 stars with luigi, then beat the final boss again, after the credits have rolled you will get a message say you unlocked grand finale galaxy