My first inclination is that I would want to tell my 12 year old self not to worry, things will work out, you'll be able to go to college, your life will work out fine.
My dad died when I was 7, which changed our financial picture considerably, with four kids in the family. I worried about how I would have enough money to get to college.
However, because I knew I'd have to foot a lot of the bill myself, I started working summers from the time I was 16, which turned out to give me a lot of good experiences. I kept my grades up and studied a lot (which was my natural inclination anyway), and that got me enough scholarships to pay for college.
Things have a way of working out. Don't worry. Follow your interests. Work hard, but not so hard you don't have time for fun.
I don't think I would have changed much about my life, honestly. For the most part, the decisions I made about the things I actually had any control over worked out all right.