Flat Head

Our 7.5 month old son still has a flat spot on the back of his head. He was a preemie and I read that this happens more often to preemie babies but am wondering what to do to help. I’ve read more tummy time and changing positions of his head and we do those things especially now that he’s more active and mobile. At home, the only time he’s ever laying down is at night and he constantly is changing his own position.

Is there anything else we can do? Will it get better over time? His pedi says she’s not worried but I dont want him having a funny shaped head all his life because we didn’t do something sooner.