I'm working on this game still and I've added a few things, including a crosshair and UI upgrades and a new map. 
The crosshair definitely helped with making it easier to pick up stuff. Nice! You didn't update the web version of the game though did you? I would suggest to be a bit less strict on the missing shots part btw, or add more pickups here and there. I fell 30 points short from being able to open the 3rd door ;-) Or maybe I should just be more accurate. Couldn't see the UI upgrades yet btw in the download version. There was a crosshair now.
I'm going to continue this game as a separate itch.io project,https://munchduster123.itch.io/zombie-game.