Call the office listed here
http://www1.pgcps.org/lottery/index.aspx?id=127716 and ask them to update your mailing address.
When you filled out the form online you should have received an email from "Application Confirmation <Lottery_Apps@pgcps.org>" with the subject line "Specialty programs student lottery application confirmation" That email includes your child's application ID number. Once the lottery results are online, use that number to find your child on the lists.