You have to mail in a reason, your info, and some money (35) within 60 days of receiving your score. You can fax it too. I'm going to do it too, just for piece of mind. http://www.lsac.org/LSAC.asp?url=/lsac/faqs-and-support-lsat.asp#19
It's under FAQ, then LSAT.
Here's what it says:
If you wish to verify or contest the machine scoring of your answer sheet after you have received your LSAT Score Report, you may request a rescoring by hand. Send a signed request to LSAC, Box 2000-T, Newtown, PA 18940 or fax it to 215-968-1277. Your request must be postmarked or received by fax no later than 60 days after the test date.
Include: your name, LSAC account number, Social Security/Insurance identification number, the test date, the test center name and code number, your reason for requesting the handscore, and payment for the $36 handscore fee (check, money order, or credit card).