Very cool game. There were some really nice visuals going on here. I especially liked the particles coming off the sides of the play screen when the screen expanded. I also liked what you did with the music as the boss advanced. It made the fight feel more intense as it went on, and the little ghost version of the boss near the end was a great surprise. Things really got heated by the final stretch.
Having three options to choose from added a nice layer of strategy to an otherwise straightforward genre. Really clever implementation of the theme, especially with the window itself shrinking as part of the challenge. Also, congrats on your first jam entry. For a first jam game, this is a really creative and polished idea.