Do you have the depth control lever (or crank)? That is needed to get it to work right. Maybe Bill Hudson will come along and help...he's the Plowing Guru!!
Your question is posted in the Cub Cadet forum, but you indicate your plow is a fast hitch (that is for an F-Cub or Lo-Boy). So, lets find out what you really have and then we can begin to help you. F-Cub, Lo-Boy or Cub Cadet?