Mary Robinette Kowal writes an inspiring post on finishing up your NANOWRIMO novel. I agree with her that the important thing, whether or not you finished your manuscript or even reached 50,000 words, is that you're writing. Because writing is hard work!
I thought I'd add some comments about what to do next with your NANOWRIMO creation. I hesitate to call it a novel, even if it has a beginning, middle and end. It's a first draft manuscript. Anyway, a few tips:
1. Don't show it to anyone. Please don't. Go and buy some celebratory chocolate instead.
2. Put it aside for a while. Or not. It's been a month since you wrote the first few chapters, and that's probably long enough.
3. Write or rewrite your outline from scratch. This may or may not resemble either your original outline (if you had one) or your draft. Hopefully, it's way better than either. Whether you use the hero's journey or three acts with turning points or GMC charts or something else, I would advise shoehorning your plot and character development into some sort of structure, at least loosely.
4. With your new outline as a guide, figure out which parts of your first draft you can keep or delete, and insert notes where you need to add new material. Rewrite the parts you keep. Salvage whatever brilliant snippets you can from the parts you need to delete. Write the new material.
5. Congratulations! You now have a second draft, although the new bits are actually first draft, of course. But be kind to yourself - call it your second draft.
6. Write a new outline that matches the second draft, looking out for pacing problems, inconsistencies, and places where you can make things even more exciting and brilliant. You should probably delete the first three chapters entirely - they are unnecessary scene-setting and backstory.
7. Repeat step 4. Voila! Your third draft. You've now removed the boring bits, fixed the bits that make no sense, untangled the plot knots, and added a whole heap of compelling character development, logically sequenced action and thrilling turning points. You've probably also deleted all those brilliant snippets you kept in step 4.
8. Edit ruthlessly for grammar and spelling. You may call the resulting work your fourth draft, especially if you rewrote a chapter or two.
9. Fantastic! Your fourth draft is possibly ready to show off to the world at large. Okay, not at large. But your mother, friends and critique partners will no longer feel you're wasting their time when you ask them to read it.
10. Repeat step 4 with any beta-reader feedback in mind. You probably also have a hundred improvements running around in your head that you came up with while your story was in the hands of your readers. Yay, your fifth draft!
11. Put your fifth draft aside for a few days and this time try not to think about it, otherwise you'll be caught in an endless step 10 loop.
12. Edit again for grammar and spelling. Polish those awkward sentences. Reconsider the chapter breaks. Change the layout to standard formatting, if you haven't already.
13. Your sixth draft (or seventeenth, depending on how long you spent at step 12) is ready to be called a novel manuscript. And it could be ready for sending out into the world at large! If so, send it out already.