5 1/2 week scam too early?

Hi everyone! I seem to not be able to find information on this. I’m 6 weeks pregnant via IVF and transferred 2 embryos. At 5 1/2 weeks they could definitely see one sac, on my left was a much smaller sac. And we already heard a heart beat which the doctor is surprised about.

The doctor said she’s about 90% sure I’m only having a singleton, but is it possibly too early? I should add that throughout my treatment, my left side was always difficult to visualize on ultrasounds. I really am hoping for twins, so I want there to be 2 in there! ☺️💗💙