Confused🤔

I’ve had ultrasounds 4 times during my pregnancy so far (13 weeks 4 days) baby measuring on point according to my obgyn ultrasound tech. Well I had a ultrasound at a free pregnancy center yesterday and she said baby is measuring 15 weeks. (I didn’t tell them how far along I am or anything. I wanted another ultrasound make sure baby was ok and growing. They do pregnancy test and if that’s positive they will do a ultrasound and get you set up with pregnancy programs and help with baby’s etc.) I’m lost am I almost 14weeks or am I 15 going on 16 weeks baby was pretty big on ultrasound machine and she did zoom in a lot. Is that possible baby grew that big. I have a appointment Thursday (suppose to be 14 weeks) do you think I should ask for another ultrasound. Also they told me placenta is on top.