I tried highlighting my dark hair and only my roots came up....help!?

My hair is naturally an ashy brown, its been dyed dark for a long while now. My hair dresser is out on maternity leave so I thought I would attempt highlighting my own hair. My roots are the only thing that came up, the rest is slightly lighter. Any type of color remover for removing a lightening mistake or is bleach my only option (beyond going to a salon obviously). If I have to go to a salon I def will just thought I would try to correct my mistake myself first. Ugh, help!!