Baby not moving in sonogram at 13 weeks and 5 days?

ok, I am 14 weeks today and I had a sonogram done two days ago.. my baby wasnt moving.. at all.. but it has a heart beat.. it says in the baby book "what to expect when you expecting" that the babies brain cant contol its body, so it moves around alot.. but my baby wasnt moving at all.. is this something to worry about??