Is it normal to have a white looking thing over the hole of a pulled tooth 3 days ago?

Common to have dead tissue, but you are supposed to be swishing vigorously with warm salt water at least twice a day, and gently brushing your gum all over the spot to help the tissue slough off. It shouldn't hurt to brush the spot, and you don't have to go buy a soft tooth brush (but make sure yours isn't all cruddy with age).
If the gum gets red is when you worry - a sign of infection.