There's a difference between thinking about it as it pops into your mind, and over analyzing it.
In all honesty, if you are questioning if it worked, if it was meant to work, is it the right thing to do....odds are, you shouldn't have cast the spell to begin with because you clearly weren't 100% sure this was what should have been done. Doubt kills a spell.
If it pops into your head, do an affirmation to increase the power of the spell or leave it up to the gods ( if you incorperated them ). Something like "This spell will work in time" or "It's up to the Gods to do as should be done". Make a positive statement, and then force yourself to think of something else.
It's difficult, I understand...but it gets easier with time. Paitence is needed in spell work.