It seems like you've learnt your lesson the hard way, so I will refrain from my instructive tone. I just hope this is a mistake you won't care to make again.
First, I would like to say, I haven't ever done an undo - spell, so I don't really know much about them, but I think you might find this thread helpful need-reversal-spell-for-love-spell-cast-few-yrs-ago-t13223.html?hilit=undo%20spell.
Finally, try to not beat yourself up too much over the mistake you made - it only adds to the negativity you get. I know it's hard, but you have already done it, can't turn back time, so it's useless to keep digging in your guilt. Cleansing might be a good idea too.
I hope everything goes well, please keep us posted.