Sort of! Really they were meant to introduce the various mechanics of the game, especially with levels 5-8 introducing each enemy type and how they function. That said, these weren't meant to be easy tutorials by any means, especially past level 5. Hopefully they weren't terribly challenging
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Nah the 9th level is the last level (And meant as a bonus quite frankly). The only levels available are the ones in the level select screen. The only other content past that "oh no" level is the endless mode, which you can access from the main menu without even beating it in the first place. The levels were meant to prepare you for that. You definitely got through the bulk of the game which I'm happy to see, and I hope you had fun with it :)