curious...plz help

Okay so it's not a huge deal or whatever but I'm curious if this had ever happened to moms before, I'm a first time mommy so it's kinda having me impatient. So when I had my first appt at the obgyn to take a test and try my prenatal vitamins, the lady calculated my days and I was 3weeks( this was like maybe a week ago or almost a week ago) and she calculated that I was three weeks and however many days, but on here and three different apps I've downloaded I was further along. I would've been like four weeks now accoriding to her, but with my apps today I'm 5 weeks. (💖😁either way I'm soooo excited). But I'm just curious has anyone given you the wrong numbers of how far along you are before? Or maybe could she b wrong? Maybe these apps?  I haven't had my first ultra sound yet due to "baby T" being so small but Ik I won't really kno until then.