I'm not sure if this is helpful, but I think if you conceptualize this story as your masterpiece that has to be perfect, you're kind of limiting yourself by setting it up as your creative end goal. Can you imagine if you finished it? What would you do next?
You can make another BETTER story. You can learn from this project and create even better characters. But you can only do that if you accept that this isn't necessarily "it" for you.
If you're not ready, I'd say go ahead and start another shorter project so you can keep improving and creating! Let go of the pressure and just make things. It's just incredible how far daily effort will get you and hopefully that would give you a boost :).