Hi ! Thanks for your feedback,Aarav.
So, after shooting all the targets , another NPC will appear named - 'Rivinson' . You can talk to him . After talking to him , the spiders will appear. Collect ammo and kill all the spiders . Then go back to Rivinson and he will give you Gold. That's it. The game ends there. I am sorry I forgot to create a win screen as at that time, I was new to Unity. And I don't have the game files anymore so I might not be able to update it. Sorry :(
FUNFACT : btw you can kill Tony Vegas , the NPC by shooting at him if you have some unused bullets. You can also shoot at empty barrels .