Hair goes through seven stages of lightening.. your around a 4.
Basically you should have left in on longer, or used something with a booster. You should have also applied the bleach to the roots last, as I am assuming you have had your hair dyed before, and your roots are new hair growth or *virgin hair*.The rest of your hair is treated already, therefore more resistant.
You can do it again, but I hate hate hate bleach, and you very well could turn yourself into cotton candy head.
Pinky is somewhat right.. when you bleach your hair, your removing pigment and making your hair shaft more porous. So when you dump a color on there, it sucks it up. Think about when you mix paint colors or even lipstick.. if you have a light shade, and you add a dark shade, its a diluted shade of the dark color..
You need whats known as a filler, you can go to the beauty supply and get a neutral filler, or a brown, or a red..you can also use Roux temporary color as a filler. Then apply your color... but apply the color to the roots last.. just as it lightened the quickest, it will also pull the color first and be the darkest..