Can i get a good score on the SAT?

so heres my story: I was in school for a couple of years, and had a little "falling out" with my parents. No idea what caused them to start getting angry all the time, but long story short, Im not in scool anymore and dont have a co-signer. When i took the sat my score was actually a little less than what i needed to get in to a university(this school required a 21; bigger schools require 23-25) They let me in anyways. I did absolutely no preparation for the act and screwed off a lot in high school. Im looking to get any scholarships i possibly can right now. Is it possible(or even somewhat reasonable I might say) for me to get a good score on an SAT>? I was also pretty average in college, so for me to get a good score on one of these tests would be pretty amazing, but what if i really studied for it? Do average people study really really really hard for it and get great scores, or am i just kinda doomed for screwing off all those high school years? what do you think. Know of any good places to start? thanks