Enter "Masutaa" as your name (in hiragana) to activate the Master Play mode. It will make all the notes hidden.

If you cant read the hiragana well, here is the sequence you need to enter it as (all directions are from the upper left corner):
Ma: Down 3 times
Su: Down 1 time, Right 2 times
Ta: Down 1 time, Right 5 times
A: Down 5 times