To unlock the final ten levels 91-100, collect all nine letters from all nine bosses throughout the game. You must kill four enemies with one Super Bubble and collect the key they drop. After you defeat the Boss of that group of levels, it will drop a letter instead of the big gem.
In order to continue from where you left off after dying in the Classic version, after you receive the "Game Over" screen, go back to the screen where you start on level 1 and scroll down. You will see the Bubble Bobble dinosaur go down on a elevator platform to stop at the last level you were at.