Well, it's not a matter of starting the songs, is that, when i took out the index from green, i need some milliseconds to think what fingers i have to move from the buttons, specially when there is a double note.
Also, i suck in fast switching from blue to red, or the reverse (syncronizing the baby finger with the middle finger, so the problem is also switching from orange to yellow). If there are single notes, there is no problem, because i kept red pressed, but if there is a double note, there are high chances to lose the multiplier.