That happened to me before. Not fun right? The best advice I can give is to wait a week or so and during that time do a few deep oil things for your hair so it won't be all dried out. When you think that your hair isn't going to be ruined if you put more dye in it , then try using the same or a slightly different blond to dye your hair again. That should take away the yellow or brassiness and make it blond. Another way is to try to blend it together by adding some streaks. I do not agree that you should always get you hair colour changed professionally; I think that store bought dye that you can do yourself if just as good as at the salon, plus it saves you time and money. Hope this helps.
Put A Toner On It!!!
I know it could be really upsetting to get another colour on your hair, when you are trying to get something else. But this generally happens when you do not pick the right colours. When you want to colour your hair it is essential that you get it done by a professional. This is because every product differs and only a professional knows for sure which colour or product will suit your skin as well as the hair texture. Now that you have already landed in some kind of mess, I would not try and give you some kind of advice that will make your hair look more horrible but the only advice I can give is go to a salon specialist and maybe they can really help you out of this. This should definitely be a better help to you rather than me trying to give you advice online.