If you're planning to take the SAT on May 3rd, the regular registration deadline has come and gone, but late registration is available until Monday, April 21st. The May exam is popular among high school juniors. Scores will be available online on May 22nd. If you aren't happy with your scores, you have all summer to beef up your skills and then retake the exam in October. Register online here. You'll need to pay a $27.50 late registration fee.
To learn what SAT scores you're likely to need to get into some of the country's more selective colleges and universities, these articles can help: