So much of writing comes down to just putting your head down and pushing. Even if it's bad, or it feels bad, or you have no idea what you're talking about, or your characters are expositing at length while you explain the plot to yourself. So much of it boils down to "Don't get it right; just get it written" and "Fail. Try again. Fail better." and "A novel is a work of fiction longer than a short story, and flawed."
Neil Gaiman blogged recently about spectacular failures, big reaches. They're scary. They're also necessary, because it's climb or die, strive or stagnate. If I'm not on the verge of failure all the time, I'm not working hard enough.
It's just that, as a person with a distinct tendency to stay well within myself, I have to remind myself constantly that this panicky feeling of being on the edge, about to tumble over, is a good thing. Because writing is not "Jackass."
If you blow it, it's not going to kill you. And you do get do-overs, as many as you want, until the deadline arrives.