Its good to admit you've got a problem, I only hope you've got the determination to take some action. When I took the SATs 6 years ago, I got a 1380/1600 my first test, then went home and took practice SAT's every night for two weeks prior to my next exam, and scored 1520/1600 on my second SAT.
Nothing teaches better than practice. Do this. Get your parents to buy you 3-4 practice SAT books, I think the CollegeBoard prints them. Each book will have 4-5 full length SAT tests, as well as an answer sheet and a scoring card to let you know what you would've scored. Then go and buy yourself those red scantrons from school and a #2 pencil. Every single night for 2-3 weeks before the SAT, take a full length SAT exam, and time it. I'm not sure how long the SATs are now, but when I did it I gave myself 1 hour to complete the entire exam, I think 1hr30 or 2hrs is fairer judging the longer SAT nowadays.
After the hour was up, I'd go over my scoresheet, tabulate what I'd score, and then focus on what I got wrong. Doing this for 2-3 weeks helped me develop all the mental tools needed to decipher SAT problems. All SAT problems follow a simple formula, and nothing teaches that better than practicing it. Its a bit of work, and will cost you a bit over a $100 bucks to buy the books, but its far more effective than a $1000 SAT prep course, and if you want to get the SATs to get into a good school, this is the most effective way to prepare yourself.