i know whats the problem!
your hair is probably porous (damaged) from eg straightners/hairdryers heat/previous bleaches/dyes/ towel drying/too much sum/not strong enough conditioning.
in this case your hair will soak up the dye like a sponge, penetrating more thoroughly, forming a darker colour and probably will take longer to fade out.
to fade it faster, try hot oil treatment (NOT the one for coloured hair), using clarifying or anti dandruff shampoo (tends to strip colour), detergent soap to wash clothes (not if your hair is damaged badly or else will get worse. rinse and condition thoroughly after).
i think the best idea is shampoo a few times with clarifying or anti dandruff shampoo, works well. after a few washes, the excess dye will have come out and you will be a good ginge. however beware that the red dye may last longer than 28 washes - even up to 3+ months if your hair was badly porous.
in the meantime, once you get to the gorge red shad definately use red colour enhancing shampoos. Te Tao red shampoo is the best and will make it a firey shiny bright red. look for colour depositing to help replace the effects of fade. good luck!