A few ideas. But first, a few questions.
Are you stalled because you just don't know where to take it? Or do you know how it ends, but realize that the conclusion doesn't have the spice it once did? Sure, a big part of it can be nerves, and congratulations on getting this far. A lot of people with ideas for a story never even get around to actually writing it. Know this--you can get the story done. You've come this far. You will finish. Don't think of it as defeat, nor do you have to sail through the ending as fast as you may have some of those sticky thickets at the beginning or middle portions. The ending is important, so it's not a bad thing to spend your time on. Also know that once you've got that first draft, you can always come back and change it. Better to have the draft and know it will need some work than to not finish at all. Get through it, give yourself a breather, and then time for revisions.
Now for the ideas.
1. Write a synopsis of everything that has happened so far. Start at the beginning and summarize it in a couple of pages up to where you are. This will help you regain a bit of focus as to what is actually happening in the overall scheme of the story, and might actually help you remember a few points that you might've forgotten along the way, ones that could help you tie everything together.
2. Give your characters some sit-down interviews. Literally type up an interview with your main characters (and some minor ones if you want) and ask them what they think of the story so far, and how they want to see the ending happen from their perspective. It can be fun when their answers take on a life of their own.
3. Write some backstory stories. One thing I enjoy doing with a character is to take them and write an entirely separate quick short story about something that happened in their life before, after, or alongside the novel I'm working on. Sometimes it helps me understand them better. Sometimes it just spotlights a part of their world I never knew before. Either way, it keeps me in that particular setting and character, but lets me expand from the constraints of that particular story that is giving me trouble. Don't let this sidetrack you entirely though. Maybe spend a day or two at it, and then go back to your main project.
4. Give yourself a short breather. There's nothing wrong with that. A day or two (not much more, I'd say) to just let the ending and all the plot threads sit in a pile. Mull over it. Write some notes. Give it time to stew. Your brain has been bashing out this story for a bit now, right? It may need to catch that final wind, but it will happen. Trust me. I know the exact feeling you're talking about, and it is simply a matter of checking the knobs on all the doors and trying to figure out which one has a tiger and which one has a lady behind it. One of them will unlock and open for you to step through. You'll find yourself wriggling with excitment and anxious to get to those final scenes as everything starts to fall in place.
Good luck, and good writing.
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