Grey and Black Gums After Professional Teeth Whitening? (photo)

It is 5th day after I got my in office whitening. Partially exposed to whitening material gums got affected and became white, than turned red. Third day grey and now it has partially black lines on the edge with teeth. Very bad smell of a rotten flash disturbingly obvious. I have visited my dantist, where he was shocked and started to calm me down that it will heal up. I'm extremely disturbed with burning sensation, dark color and bad smell. Please help!!