Hi I am 31 weeks and I think I am more because I had a 3d ultrasound at 26 weeks and they told me that the baby's head is measuring at 28 weeks. I said this to my doc and she just said no that I am due on the same date my last ultrasound is this week and going on what I am reading I feel about 33 weeks, so is it possible for the first scan to be wrong

Not very likely at all... it is quite possible that your baby is just large... not trying to scare you or anything but I had a 9lb 1oz baby on the first go and my second child was 3 weeks early and 8lbs 3ozs... remember that measurements are just a guideline of where the average baby should be at your stage of pregnancy... but there is no set size... I can tell you that my sons head was rather large and I had to be cut.. my daughter was much smaller in diameter as far as her head goes and she slid out easy no cuts or tears... every woman is different and every baby is different... your doctor measures your stomach at almost every visit... if he/she felt you were further along then you were they would have said so..