Taking the sarcasm out I agree with bloovee.
USB is open ended so it's easy to caution anything for USB. Good refereeing is about useing USB for incidents that are not covered but is necessary to caution. OP was not necessary to caution at all. Not mandatory, no impact on control or fairness. The team was punished enough by having a goal disallowed.
Sometimes it is tempting to use an unnecessary card to put assurity on a controversial decision (I have done it), I think OP was one of those.
Saying that disallowing a goal is 'punishment enough' is total rubbish. The taking of the free kick is what is being punished and has to be done accordingly, whatever happens with the ball as a result of taking it is irrelevant to the punishment. If he had missed would you then have given the booking?