4 weeks 6 day Ultrasound. Help!

So I’m freaking out because at my first appointment they did an ultrasound when according to my ovulation (confirmed one) I should be 4 week 6 days, but he assumed/said I was around 3 weeks. This is the pic and it was an abdominal ultrasound (no transvaginal which as far as I understand gives a much clearer picture). Only the sac is visible ( the small black dot just in the middle). I should go in 10 day to check the progress. But I’m scared that he dates me earlier then I’m. Please share your thoughts