High HCG levels

I’m 6 weeks pregnant today,Yesterday I had pain on my right ovary, so I call my doctor and they ordered blood work, they find very high Hcg levels.

They did an emergency ultrasound last night, they find the baby inside my uterus and they schedule another one next week, I thought I might be pregnant with twins, but the one who did the ultrasound showed me only one baby and one sac,

Why do think she ordered another ultrasound? Do think it could be twins?

Anyone find one baby then it was twins?