If you'd like to have your answer sheet rescored by hand, it'll cost you $50. However, if at least one error is discovered, the College Board will refund the fee. You have up to 5 months after the test date to request this service. If you'd like to take the $50 gamble, call the SAT Program Customer Service at (866) 756-7346. The College Board will send you a "Request for SAT Score Verification" form, which you will have to fill out, sign, and return with your payment. 3-5 weeks later, you'll receive the results of the hand-scoring and a refund, should you be entitled to one.
The College Board website warns (scroll to bottom) that your entire answer sheet is re-scored and that the outcome can raise or lower your score. The adjusted score is final. From my experience, few students receive a higher score through this appeals process, and few get their $50 back. If you score much lower than you expected, you may want to explore this option. However, if you're simply not happy with your score, it may be time to accept the results and start preparing for the next test date.