i can't really help you out, but i feel that i have to tell you that every relationship must have a certain level of trust to work. By her thinking you don't smoke weed, and you being too scared to tell her you do, that's a breech in the wall of trust. Try to avoid those, and be completely honest, even if you feel like it'll hurt your case, because in the end, they'll care more if they know you're telling the truth