My hair was highlighted blonde and it was really nice, but I fancyed a change and had it dyed back to brown, however, its gone really dark almost black and there are patches at the back where my blonde hasn't been covered... I know that something shouldve been put on my hair before dying it but it hasn't and I'm stuck.
Please help
I'm only 15, this could really affect my life

Hi I'm no hairdresseer but when ever you dye over blonde to go dark you need to put a red color on it first then put brown over the top. As you have already done this I would suggest you go to your local salon and ask them first. Don't worry mine has been alsorts of colours were I got it wrong we all do it.

Gooner28 is right. When you bleach your hair it takes out all the pigments. And when you apply a dark or brown hair color over bleached blonde hair, it will look muddy or appear even darker. In order to go from blonde to brown, you will need to use a color filler that contains a red base and then apply the selected color. You should go to the salon and have them fix your highlights.