This has a lot of potential. You've done a good job of creating a tense and vulnerable situation. Having large open spaces that you don't know how to navigate is intense and works really well. It's too difficult though. You might want to put in some more ammunition, give hints when the enemies are coming for you, such as footsteps, and make the instructions more clear.

Nice concept but it feels like it's missing something.

Excellent level design, I can't believe this is your first game.
The more time I spend making games, the more I appreciate level design like this.
I had a couple of performance issues but that's probably just the laptop I'm using.