You implemented the theme well. Couple of things that I notice: The sound of shooting during the tutorial is too much.. maybe put another sound.. Also I notice that if you play again you player rewind from previous game .. this is an screenshot .. you nna notice I have 10 ammo and the rewind is already showing up.. 
Viewing post in Agent Bullet jam comments
The appearing of the past agents are actually just random. According to the logic of the game , those were the bullets u shot before the game started. You obviously didn't start shooting with 10 bullets. He wasted a lot of bullets and rewinds time to get them back according to the story. It does not depend on your position. If it did , the player can easily camp at a single spot and get all his ammo back. There is no rewind in the actual game mechanic. Instead it is used as a story part. Anyway , thanks a lot for the feedback.