Don't worry, everyone sucks at first. Remember: the editing process is just that - a process. No great paper (or article, or novel, or tv show, or movie) got that way without substantial editing and revision. The best thing you can do (and most impressive) is to turn this sucker around fast and give the attending something to look at. I've found that it takes much longer for me to obsess over a manuscript than it does for me to just write something and get it to my PI for editing. Once you hit that point, the rewriting process begins, but that always seems to go much faster because it's far more goal directed than the initial write. For example, rather than the vague "write up this case," it's much easier to address something like a comment that says, "give more detail about initial physical findings and be sure to mention the initial bedside endoscopy and its findings." The back and forth is actually the best learning experience. Nobody expects a student to churn out perfect papers on the first draft.