Wow, that was hard! I liked the graphics, and sfx and music helps to create a tense atmosphere. The presentation of the game, tutorial included, was very good. Different types of enemies and the number of mechanics implemented help the game to feel complete. Which has a lot of merit in a jam (and using Scratch!), so good job on that; I know it's not easy to finish a project like this one in 72h---even less if you do it alone.
Just as constructive suggestion, I think that there are two options that would round the game. The first one would be to keep the level of difficulty similar to what is now (that is, very high!), but implementing a "quick-restart" shortcut and a highscore system of some kind; I think in this way the player would be more inclined to keep playing. The second option would be to ease a bit the speed of the game, or lower the number of enemies, etc., at least in the early phase of the game; so it has a slower / softer start.
Good jam! :)