rule number one of nanowrimo: never read over anything you've written until November 30th! lol, the point is to just write, not getting anything worth reading out of it, if you're lucky you end up with somehting worth holding onto.
I don't think you should give up. I know some people have scrapped what they've written and started over.
No, you have to write something new. It can't be something you've written and then copy and pasted.
I took an old idea I never got around to writing and went with that one since I already knew a little about where I wanted to go with it.