Fetal pole size

When I went in for my first ultrasound I was supposed to be 9 weeks but he saw an empty sac. 5 days later I went back and my levels had went from 11000 to 20000 in 2 days. He saw a gs, yolk sac and fetal pole as well as heart beat. He measured the fetal pole and said it was 0.25 cm and I was 5 weeks and 6 days. According to glow the baby was supposed to be 0.3 in. Does the 0.25cm measurement sound right for 5 weeks and 6 days? I am 7 weeks today and I don't go back until the 23rd so I am a little nervous about its size.