It depends on the kind of spell. If you want a specific person to fall in love with you, then it won't work... unless those are his true feelings for you.
If however you use a spell (and since it's a new moon love spell I think so?) to influence love in your life, to have a general request like "I want to find the one that is mr. right to me" or something like that.. then it will work.
Did you transfix it to 12 days though? Not sure if the universe will listen to that... ;)