Big baby or further along?

So yesterday I went to a 2d ultrasound place. I had a blood test done last month and it came back saying it's a girl. I had some doubts because I know someone who was told one thing and ended up being another. BUT it's definitely a girl. However the ultrasound tech told me that she's measuring 15 weeks and weighing 4oz I'm 14 weeks and 3 days. She said her calculations for my due date is January 25th. My doctors calculated due date is January 30th. Not too far apart. My next appointment is next week. Just curious if anyone else went through that. I was a big baby and my son was too the tech said it's early to tell whether she will be big.