Hällochen,
The Shrink Mechanic is well executed and works fine. I would recommend havin the bullets disappear, once they exit the screen. You can easily shoot all enemies, while they are off screen, if you know where they are. Also, a tutorial of some sort would be nice. At least, a quick description of the controls on your itch.io page (You can still edit your it)
Its really sad that the game isnt longer, because the mechanics you got down.