Pew pew pew pew pew! Great job making a top-down shooter-type game. Haven't played one of these in a while. I think it might be improved by adding some contrast between the bullets and the background as well as some contrast between the collectable pins and the background. They're a little hard to see in some settings. Maybe shadows beneath them would help? I did read the directions, so I knew to fly up, but you might also consider adding an indicator at the top of the screen telling the player to do the same when they get all 5 pins.
Almost lost at the boss, but I managed to sneak a win!