Culprit here!
We intended to have more levels between the 3 you played, but didn't have the time at the end to make them at the same level of quality for the set dressing.
So yeah, if it feels like the difficulty ramps up quickly, like if you skipped some levels, it's because it is, sorry about that :D
However, I'd say that I'm happy we put a quite challenging level (the last one) at the end. It gives the game some replayability and allowed me to brag about my perfect score in 1:33 sec :D
For the boost, we picked this option to try to fit the jam's theme, but if we were to continue the work on this game (which we could ^^), we already planned to let the player fix/improve their plane and change the engine behaviour ^^
Thanks for playing and for your super nice comment!