You have asked a theoretical question and you have gotten theoretical answers, some say 'yes' and back it up with scripture, some say 'no' and back it up with scripture, and we are all brothers and sisters in Christ. Maybe I'm wrong (and a far-out hippy!), and I'll have to learn better. But my hope is in Christ, not in my own rightness.
But here's the problem: You are not in a theoretical situation, you are in a real life situation. And real life situations have real life people who react in real life ways.
You say that your fiance doesn't think that the two of you should get married until you have 'enough' (whatever that means to her). Well guess what, until the two of you have 'enough' she is not going to consider herself married to you.
She might, with enough coercion, decide to go ahead and get married 'in God's eyes' before getting married 'for real', but that won't change the fact that until that wedding happens, she won't feel married 'for real'.
Right now, your love for her is all sunshine and bunnies, and she, no doubt, thinks that you are the bee's knees. You guys are invincible, absolutely immune to whatever it is that causes all these other poor souls to split up. It's a wonderful feeling and you should savor your crazy love for each other.
But it gets crazier. At some point, the real world starts moving in on you, and you are gonna have to start truly sacrificing one for another. It's hard. This is when the sunshine and bunnies hit the fan. And it ain't pretty.
This is why half of the people you know decide to 'shack up' instead of getting married, and this is why some of your peers are already divorced. Do you think they didn't really mean that thing about 'till death do us part'? They did mean it. They just couldn't back it up with the soul-stretching work that love requires.
So what happens when the bee's knees start getting creaky, and your fiance tells you, "this was a mistake, we shouldn't have done this", and she packs her bags and she leaves? You will have suddenly gone from a 'husband' to an 'ex-boyfriend' in the course of one conversation.
You may know that God takes your vows seriously even without the white dress and the paperwork, but she does not, no matter how cute she thinks you are right now.
Be careful that you don't find yourself in a marriage of one.