[racket] How write regexp for lexer

Hello. I need write rule for lexer for recognize comment which begin from first column of line. 
I have next regexp for comment (:seq "//" (:* (:~ CR LF))), aftrer add cr/lf to begin of expression i write (:seq  LineTerminator (:* (:or #\space TAB FF)) "//" (:* (:~ CR LF))), but this regexp -first eat LineTerninator, second - don't recognize comment if it first in file
Help me, please, write this rule