Help! I'm confused

Jennyfer • currently pregnant with baby #2. Mother to my 3 year old.

I went to the doctor today for my 1st I

Ultrasound. LMP says I should be 5 weeks but the doctor said that the Gestational sac measures 3 weeks. He says everything looks like is in order. Should I worry? I won't see him again till September 10th. Anyone went through this and had a healthy pregnancy?