Into the Wild - AQA A level

I've done a recast on the character Butch Killian from chapter 2 of "Into the wild". My teacher has graded this at a Level 3 (Grade C). I Would appreciate if someone could provide any improvements:

I was riding my ATV out near the Sushana when I spotted two guys standing by that rusted-out old bus. straight away I could tell something was off. They looked gone, nervous. real shaky. Even before I got close, the smell hit me. Heavy, rotten flesh — the kind of smell that don’t belong in the open air. That’s the kind of smell that tells you somebody’s been dead a while.

I stopped the engine and everything went silent. they kinda just, just stared at me. Didn’t say a word. nor did they need to — the stink said enough. I nodded and walked toward the bus, refusing to breath from my nose. I already knew what I was gonna find.

Inside, it was worse. The air was thick, rotten. I saw the sleeping bag in the back, zipped up, and right away I knew. He was long gone. Could see it in the color of him, the way the bag sagged. No one had to tell me.

Samuel (the older one) insisted we need to move the body, get it out of there ASAP. I told him bluntly, “That’s not our job. leave it for the Alaska State Troopers.” He didn't argue nor question me.

I turned to them and said, “I’m going for the radio.” Got back on the ATV and headed for the highway fast as I could. When I finally got on the radio, my voice was stumbling. “This is Butch,” I told them. “You need to call the troopers. There’s a man back in the bus by the Sushana. Looks like he’s been dead for a while.” They said they’d send someone out.

When I got back to the bus, Samuel (the older one) was saying we need to move the body, get it out of there ASAP. I told him flat, “That’s not our job. That’s for the Alaska State Troopers.” He didn't argue.

We built a fire that night and sat around it, eerie. No one talked. That smell kinda just sat with us, hung around. It was like - it had a weight to it, a heavy weight. We waited, not saying much, waiting for someone or something to come for him.

When we finally heard the chopper coming through the trees, it was 8:30 in the morning . I felt a sense of relief.