Murfie gave you a good way to simply take away the energy built up and directed upon the desire while it isn't exactly a full cancelation of the spell itself since the spell has consequences and affects which are already done. Meaning that it isn't that easy to destroy and take away what you've already caused by casting the spell.
You can easily get the conclusion from what I've said above that reversing the effects of a spell that is done successfully is quite impossible. Spells typically work with natural order and if have been done successfully they have an eternal marker on what they affect.
reprieving, ceasing, dissolving, neutralizing, or countering your spell is basically what you're looking for. Even though energy can be banished and won't stay around forever, there are still resulting outcomes.
As Murfie said, it's important to get rid of the energy you directed upon the intent specifically. What you also need to do is not to target the spell, but to target the resulting outcomes.
You may cast a spell for piece and for a better result for ever individual outcome or all of them put together. It's your choice. Praying for forgiveness and for better ending is always helpful to your emotions and the affect that may come by... Remember that the energy will not be around forever and it won't always play a big role in your life. Energy comes, and goes.
As long as you try to fix what you've done by working for it personally by your own way and keep being positive, it should be fine.
However please bare in mind that it's not too easy to fix something which typically goes with nature and has been already done. You need to work for that, and slowly take steps to make the situation better.