Head down???

Im almost 31 weeks and im worried that my son wont go head down in time. I know i have a few weeks left, but i just feel like he wont do it. I had a ultrasound last week and he said it looks like hes favoring this position because his head has more room... When did your babies turn head down?? What can i do to help him turn? Will i have to havea c section if he dosent turn?