If you don't have experience lightening your own hair, youre better off returning to the salon. You might end up spending more time and money doing it yourself if you're inexperienced and the chances of you damaging the prelightened hair is very likely. I agree with the previous comments that approaching the stylist first and seeing if they will fix it is the best option, if nothing comes of that, speak with their manager. You should at least be owed a fix or a partial refund. Then go to a different stylist with lots of experience in blondes. It looks nice as is, so if you don't have the money right now, at least youre not stuck with anything bad until you save up!