Question about Henna Tattoo?

So i got a henna tattoo that is on my back shoulder blade and slightly over my shoulder on my neck/chest area. I got it 2 days ago and the paste hasn't flaked off at all yet and if i accidentally touch it too much or have something rub it, it smears a little so its still soft. Also i was checking to see if the lady who did it used black henna and i wet a small portion of the tattoo and it came out a indigo/purply color on a q-tip. Is this bad? and how long should i leave the paste on because it hasnt flaked yet...