quick question about gestational age!

so when i had an ultrasound a few weeks back, the baby measured 4 days behind the estimated date from my period. I thought I was at 7 weeks but instead i was at 6 weeks and 3 days! i changed the date in this app, so now it says the baby is 9 weeks and 6 days, but when i went to my OB today, i was told that the baby is 10 weeks and 3 days. should i leave it pushed back or change it back to the original date. sorry if this is confusing! i just want the information based on gestational age lined up so i can learn about the baby’s development while it’s happening! thank you. (-: