Henna on hair??

Hi, My parents won't let me dye my hair because of all the chemicals and the stuff it does to your hair but they are allowing me to put henna to "dye" my hair. because it's natural. My friend got me this pack from her asian supermarket and i tried it but it didn't show up. My hair is slightly brown, is that a reason why? How can I get the henna to show up? Do i need to "dye" it weekly or lighten my hair naturally in some way? Please advice.

how long did you leave it on for?