Could this be twins?? Worried

So I went for my first appointment and they did the normal but said my hcg was really high and asked how far along I thought I was. I knew I had to only be like 5-6 weeks so they did a ultrasound I guess to check. And I have been stressing because they had two people come in and look. And said everything looked fine but I wasn't as far along as they thought only measuring 5 week 5 days like I thought. They want me to come back in 2 weeks for another ultrasound???? Why?? I never had ultrasounds this early with my daughter. Could something be wrong or did they see maybe more than one but not tell me idk I have just been worried because this pregnancy all the way around has been different with symptoms I have had little to none. I just want it healthy