Honestly, anyone can learn to be a decent writer with a little bit of practice. Right now, my advice would be to take some time out of your day, sit down with a pen and pad of paper (handwriting is better than typing for this excercise) and just start writing down anything that comes to mind. It doesn't matter at this point what you thoughts are, it just matters that you are putting your thoughts on paper. You could talk about the weather, how much school sucks or how dumb you think this exercise is, but as long as you are putting pen to paper you are building confidence in your writing ability. Trust me, you can learn to become a good writer but not without actually writing something.
Once you get writing, inevitably your mind will wander toward the topic of your essay. This is a good thing. Keep writing until you have nothing to left to say. Don't worry about structure, grammar, sources or any of that kind of thing yet. Don't worry about being redundant either, just make sure you are expressing your thoughts and explaining your position as clearly as possible.
After you finish, type up what you have written down, but only those things that are relevant to your paper. I think you'll be surprised at how much you actually had to say. Now your are ready to actually begin editing, sourcing and structuring your paper, but you've put the "OMG I have to write how many pages!?!" anxiety behind you.