I feel bad for all the admins on this site having to deal with really poor stories being sent in. For my last few pastas I have been using a free website to help me out--
It's a really good site. It's free and even grades your paper (it a guess but it's close, I've tested it with my college work and its greading is either a few points off or right on the money). Now this is in no way a fix all, it's still a computer taking guess', you still need an understanding of English. This is more for people who find it easy to correct others work, but hard to find the errors in your own.
Also don't worry about the agreement part, I read the thing, you're not giving away your work in any way. I hope this can help others as much as it has helped me.