What I see so far looks promising. I kind of like the movement pattern of the enemies. Feels a bit unfinished, but for a 3 day game jam the result is pretty solid in my opinion.
"The bullets interacts with the zombies by decreasing its health; the zombies interacts with the player by decreasing its health; and the score interacts with the zombies' spawn rate and speed." - Fair enough.
The projectiles are so fast that they can fly right through enemies without hitting them. If you need them to be this fast, they should use a raycast to make sure they don't fly past anything.
Overall good job! Hope you enjoyed the jam. :)