Stressing out! Was told to come back at ultrasound

Tiara
I had my mid pregnancy ultrasound yesterday and the baby was facing my back however they were able to tell me the gender.. Boy! But they want me to come back in 2-3 weeks. They said it's because they couldn't get proper pictures. Has this happened to anyone else? I'm thinking they have to confirm if something is wrong. HELP! I'm freaking out and the ultrasound isn't for another almost 3 weeks :(