I don't know if this works for cancelling spells but I guess you should try at least.
You need:
Pen
Paper
Candle&Matches(optional)
Get yourself prepared, meditate before this if you want. Now write your wish down on the piece of paper. While you're writing it down visualize your outcome working. Once you're finished, fold the paper towards you. Get your matches and burn the piece of paper. But if you don't want to do that, either bury it or throw it away and just forget that you ever did the spell(or at least try not to constantly remember it).