Lizstraw, when you get to the point in your manuscript where you feel like you are just spinning your wheels and getting nowhere and what you are writing is worthless, Linda Joy Singleton calls that, "Muddling through the middle." That's when she advises writers to "give themselves permission to write crap." And you just keep writing right on through it, no matter how bad it is. Don't worry about revising it as you go, don't worry about whether it's good or bad, just write to the end of the story anyway. Often, when you go back and look at what you wrote, you will discover it wasn't as bad as you thought it was, and if it was? That's what revisions are for. You can always take the lump of clay you wrote and mold it into something perfect later on. But until you have the entire lump of clay written, it's not possible to shape it into a salable manuscript. So just remember you are currently, "Muddling through the middle" and keep the words flowing - good, bad, or indifferent.
Happy writing!