I can understand your concerns,Hydroquinine one of the constituent of the cream has hyper pigmentation as a side effect in some patients.
So may be thats one of the cause,but i didnt get from your question that earlier before the application of your cream by Black Scratch you meat a bruise
if its a bruise then you can leave it alone and give it sometime .
Anyways you must consult your dermatologist
again and discuss it,and i would advise to stop applying the crean till then.
i hope you ll find the answer helpful,
thanks very much and all the best.