Re dying my hair after 2 days.?

i had lightbrown hair and some highlights on top and i wanted to get rid of them and dye my hair a darker brown so we went to Walgreens and bought some shampoo dye, now my hair is black :/ it's been 2 days since i dyed it and i dont like it at all. We bought some real dye at Sally's and i was wondering if that'll kill my hair? I have thick hair and its usually pretty soft and its not long, its kinda like Zac Efron or Chace Crawford. Any help? I really need to get it dyed before wednesday and its tuesday today.