Some people's hair is too sensitive to dying to be able to be dyed.
Even with semi-permanent hair dye.
Sometimes the dye'll stay with the hair a bit longer.
I dyed my hair black last year and the first few months of this year it looked terrible.
I've let it wash out and now the areas that looked thin have pretty much grown back to what they were before I dyed it.
the hair near my sideburns is still tainted with a bit of black and is still pretty thin.
eventually the rest of the dye will come out of your hair and it'll grow back thicker.
No worries, man.