Faint White Mark on Black T-shirt from Iron?

A hot iron was accidentally placed on a mattress. The satin on it stuck to the iron in sticky form. Unknowingly, I placed the hot iron on a brand new black t-shirt and got a white mark. It looks more like small white dust particles. I don't know if I burnt the t-shirt or is it the sticky mattress substance that came to iron and then to t-shirt. I tried to wash it, but it did not come off. The T-shirt material is 100% cotton. Will dry cleaning help? What should I do? :-(

By in_silence_2k