I'm not looking at it right now, but I thin you play as Kong about 4-6 times. So if you've only played him once, you probably have about 10 chapters left. Some are just 2 minute story fillers. It's a short game, but still a lot of chapters.
If you're getting sick of it though, why play? For achievement points? pishaw
As for not having any bullets, always grab a spear anytime you see one even if there is nothing to kill. Then when there is something to kill, that spear will give you your first kill. And if possible during a fight keep using spears. Spears run out too, but you can grab them out of dead bodies if you do it quick.
Also, use the bones from any bone pile laying around. You can stand right on top of one and keep on grabbing more and more. I've never had a pile run it, so I don't they can. That's what I had to do on the Brontosaurus chapter. Too many dinosaurs kept coming out of nowhere. So stand on the pile and let the dinosaurs come to you. If they get to close, back off and use your gun, but otherwise use spears and bones whenver they're around. After you've killed a dinosaur, grab another bone set it on fire and move on. Light any fire pedestals as you go. Also burn any brush so you are not restricted in your movements.