My personal choice is to never, ever scrap a first draft. No matter what. As an author, often I'm so close to the work that I have no idea what's good and what's shit. A first draft is the party draft...don't worry about what's good or bad, just get it out. There's always going to be ups and downs during writing, especially in a longer work.

Stick with it, even if you're not having fun. Make a wild plot change if you have to--during a first draft, you should tell the story you want. Get it out, then let it sit for a while. Do something else, if you can. Only then can you judge your work with an objective eye.

Did you completely delete your old story? How many words have you gotten out? If you're over ten thousand, I'd say see it through to the end. Then, only when you're ready, let someone whose judgment you trust read your work and find the holes for you.

Good luck! Don't give up. I'm certain you're being super hard on yourself--writers usually are.