Colour Correction Help Please!

Hi guys,

I've been dying my hair blonde for years (I'm naturally dark blonde with a lot of red in my hair) so that's why I thought I'd try a corrector tone in order to get a more grey/ashy colour.

I used Wella Koleston Special Mix Intense Pearl 0/88 and mixed it with 10 developer. I'm wondering if I used the wrong developer (I actually mixed 20 volume developer with water in equal parts), and the solution looked a greyish colour, which later (I've just looked) turned BLACK! in the mixing bowl..

I left it on for 5-7 minutes and washed it all out as my hair looked frighteningly dark. I'm now left with a light black colour, with my original hair colour coming through in the undertones.

I'd really REALLY appreciate someone helping me on this. What do I do? Will it fade out within a month? If that's the case I could live with it, but at the moment it doesn't look like it's going anywhere. Will I wash my hair repeatedly to remove it, or do I need to bleach?

Please help guys, Thank you