J.C.
I would wait to see what you measure in the next few appts before thinking your dates are different. The baby's position can effect the measurement. Say the baby is really in front so a bigger curve means more centimeters than if the baby is a little off to the side. Does that make sense? The big difference in lung maturity happens between 36 and 37 weeks. Many more kids at 36 weeks have lung issues than at 37 weeks. Keep telling the baby s/he needs to grow inside until at least 37 weeks!
Also, babies grow at different rates so you could measure ahead and then be right on for your original date.
The real bottom line is to make sure you're eating really well(harder to focus on with a toddler!), get sustained exercise, like pushing your toddler in a stroller, minimize stress in your life, and trust that your body, the baby are healthy!
Good luck!
J.
mom of 2, 21 and 15; RN, IBCLC