I was in that same situation when I was in college. I was accepted, early admission, to one of the most expensive schools in the country. I wound up not being able to go because I couldn't afford it. I was happy, in some ways, because the state school I went to instead gave me a full scholarship and I have no student loans. I was able to buy a house in my early 20s.

So just some random ideas based on how things worked out for me:

Try to find out if a particular department or branch of your school gives out better scholarship money. I learned too late that I could have gotten a free ride if I had applied to School X rather than School Y (both within the same university system).

Reconsider getting married to a major now. I was dead set on my major and wound up switching to something else a couple years in.

Don't limit yourself by only applying to the one school. See what other deals are out there. I had no other options when at the last minute I learned that I just couldn't swing the cost of the early admission school. My parents wouldn't take out the loans (and probably wouldn't have been approved anyway) and as an undergrad, you are limited to 3k a year. I had no choice but to go to the state school at that point-- and my financial aid the first semester was awful since I applied late.

Start asking everyone you know if they know anyone who has something to do with your dream school. A friend's father knew someone on the board at my dream school. I may have gotten a better scholarship package because of that, but it still wasn't enough.

Try to establish a relationship with the professors in your department. Get your name in front of them. Personal connections will really help. Find some alumni of your target program and network with them.

Fill out all financial aid stuff the very day it comes out. This makes a BIG difference in your award package.

That's what comes to me at the moment. I hope it all works out in your favor!