First of all, it's awesome that you're so close to completing a project. Even with all of the mixed feelings attached, it's going to be one of your own ideas that got to live out its life from start to finish and that's pretty cool!
I totally get that feeling with so many of my characters. I feel like I'm recording their key experiences and not only that, but I'm compelled to do it for reasons I can't explain. And yeah, it's helluv frustrating when you can clearly see and feel everything about their stories, but you just don't have enough of the right words to express it the way you see it in your head.
For me, if the words are too far out of my reach, I put the story on the backburner and just lend my efforts to the stories I can almost get there with. There's also the chance that you may come back to your story in 6 mo to a year and suddenly know the best way to edit the wording in a section that used to give you a hard time. That happens to me pretty frequently too. It's like present me kinda of knows what to do, but future me has all of or at least more answers.
in the end, you're right. you can only get better. writing truly is a Process over a product.