Sometimes when you get that stuff, it isn't very good. It could have been on the shelf for ages. I'm glad your experience wasn't horrible but I'm sorry it was not as good as your hoped. Go here:
Henna for Hair and read some of the good info they have. They are a very good source for PURE, fresh henna and they give instructions to the letter about how to mix and apply and things that hinder your process.
Here is a great free e-book on the process:
Henna for Hair
They even have pics of what the color looks like on our hair types. You should mix the henna with something acidic (lemon juice, apple cider vinegar, orange juice, etc) to obtain dye release. I use OJ. I know folks add other stuff in there but I never have. I just use the pure henna and the OJ. Anything else, oil, eggs, you can do AFTER in the conditioning process. That's just my opinion. Others swear by it but I am going for color (first), conditioning (second) and those things (although they are conditioning), do not help achieve max dye release.
I did a fresh one a few days ago and if I get the energy to do my Diva Smooth before this stuff grows out, I will put a few pics in my blog. I go for gray coverage - not redness and use both henna and indigo. Don't be afraid to try it again.