I liked the game, though I found it a bit too challenging! It's always really cool to see how much can be done with Scratch, given some of its constraints. I really liked your health "bar" heart, and I think my favorite part was the little cutscene between the tutorial and the battle.
It seems like there's a brief invincibility window after getting hit by a bullet; it would have been nice to include a visual indicator for that. Alternatively, I think I would have actually preferred to have no invincibility window, but have each bullet keep track of whether it's already hit the player to ensure you can't get hit twice by the same bullet.
Another suggestion would be to include some measure of progress. I had no idea and personally never got far enough to know whether the game was meant to be endless or not.