U/S's are usually off.
Your body will grow the right size baby for you no matter how big the Dr, or U/s technician says it's going to be.
If you are seriously worried about too big of a baby, just eat less sugar, carbs and refined foods until the due date.
Eat as whole foods, as you can. Focus on plenty of protein, veggies, whole grains and fruits.
An average woman's pelvis can EASILY push out an 11 lb baby, so I think you'll be ok.
Besides they can't just cut you open just cuz the U/S says it might be a big baby. They have to ask your permission first, and of course you'll say "NO, I can do this on my own, thank you very much."