I dyed my hair with Casting Creme gloss: plum 316?

I dyed my hair with this yesterday and am happy with the result! I've got naturally dark brown hair and it looks good, but I want to know will it wash out in 28 washes like it says it will? or will it fade and stain my hair an odd red colour? and if it doesn't come out what can I do? I don't want to have to go to the salon to get it done! could I just dye over it with a semi permanent dye thats my natural colour? please help! thanks for reading :)