I think your writing is good enough, in terms of being in character. For your age, you're actually doing pretty darn great. The only advice I feel inclined to give is to beef up on the imagery and learn how to use a few more types of punctuation (I will elaborate more on this).
For now, here's an edited version of your passage (I will underline my changes):
They took me. They took me away from my home, my family, and
everything else in my life. How could they treat us like this? Like
we're worthless animals. Do they even have hearts?
I remember
the long sail here. I sat there, surrounded by other unfortunate
victims, only millimeters away. There were rows and rows of bodies.
Battered bodies. Bruised bodies. Holding my breath had been pointless; the
pungent stench wouldn't go away. I can still remember the distinctive
scent. The cries so loud that they still echo and ring through my ears.
The
condition in this small room is terrible. Twenty of us squeezed into
such a tiny space. Perspiration runs down my face. It's so hot in the
room, barely able to move.
My stomach growls with hunger. We
barely get to eat, and when we do all we get is a small handful of rice.
Some refuse to eat because of so much stress I think they'd rather die.
So would I.
Okay, so first of all, comma rules. Gotta put one at the beginning of everything that could be a sentence all by itself. Gotta put it when there's an introductory word or phrase. Gotta put it between every item in a list that goes more than two things, and that includes before the last one, even when there's an and. Example: I like pie, cake, and ice cream.
Also, semicolons. You can use them to separate two sentences without using a period or a comma and a conjunction. Like in this sentence: Holding my breath had been pointless, the
pungent stench wouldn't go away. The comma was incorrect without the word because. So, you can either add that, or do what I did, and add a semicolon.
And now for my favorite part of what I have to say. Beefing up the imagery. I don't really know how to explain it, so I'll just re-write one of your paragraphs my way.
Original: The condition in this small room is terrible. Twent of us squeezed into
such a tiny space. Perspiration runs down my face. It's so hot in the
room, barely able to move.
My version: This room is truly dreadful. There are twenty of us crammed into this tattered, musty, dimly-lit box, leaving me with barely enough to reach one hand up to scratch at my nose with gritty, split nails.
It is hot in here. It is so, so very hot. I have been here for hours, as everyone has, waiting and waiting for someone to come deliver us to our hellish eternities. I am held in a sweaty purgatory as I do my best to scribble out this message to no one, perspiration trickling from my brow, and clothing effectively stuck to my skin. This prison smells like bodies (dead and alive alike) and breath.
Sorry if I went overboard >.< I really need to learn some self control. I hope I helped.
