@Cuban-curl-E: WAIT until your too-dark hair has faded out. I know, it's hard, when one wants to correct something yesterday and all. But if you DON'T wait, you risk messing things up further. Haircolorists make a lot of money off of home color jobs gone bad, usually when one tries to fix something at home without knowing what they're doing. If you let your hair lighten up(and that can be moved along by using Prell shampoo a bunch of times along the way and of course using a really good conditioner since such a strong shampoo tends to dry out the hair)then you will notice the effects of the Goldwell product, since it ADDS pigment. This is different from traditional permanent color that lifts virgin color out of the hair and lightens if using a lighter, brighter color than one has naturally. So do definitely wait before doing anything!
With a demi-permanent color like the Goldwell, it's best to pick a couple of shades LIGHTER than one thinks one wants, due to the fact that it deposits color. In this case, maybe a light auburn or brighter copper, with a little bit of a brown mixed in(like 1 part of that to 3 parts of the red color). Best of luck!