Thanks for the reply. I use W to jump because i'm not used to jumping with the SPACE button. About the starter enemies, they have ability to avoid player's ammo so it's kinda hard to hit them with the pistol. But you can upgrade the pistol in the shop. The price is affordable (i think). About the empty space on 1080p screen, maybe i will improve it in my next game :). i stop working on this. (sorry).
Edit: you can adjust the screen resolution to 1366 x 768 to get the fullscreen game. I'm will improve this later.