Hi, thanks for playing my game!
The boss is indeed unbeatable, but it's possible to run away from it. You simply need to keep firing at the tentacles moving toward you while maintaining maximum velocity. You win when you're far enough away from it. Without proper guidance, this can indeed be a bit confusing for players. I admit I spent too many time on the aesthetics and world generation, and the actual gameplay feels a bit rough around the edges :p
As for the file size, thanks for pointing that out! This is my first time making a game using Unity, and I exported it at the last minute, so there's definitely room for optimisation. I'll keep that in mind if I continue developing this project in the future.