There is a great product you can use that will fix this for you called COLOR OOPS.It is sold in stores such as Rite Aid.
It will remove all artificial color,leaving you with a clean slate to start over.
Be sure to follow the directions EXACTLY,because it's very important to rinse it out like 5 or 6 times.I have used it a couple times when I have colored too dark.(doesn't work if you went too light) and it is a lifesaver!
Also,it is not damaging at all,only bad side effect is it is kinda stinky.It has a sulfer-rotten egg smell.
You can re-color the same day that use it.(I would wait at least one day though)Good luck!