Could they have missed a twin?

I had my first transvaginal yesterday and they said I was measuring a week smaller which based on the math doesn’t add up. I had a positive ovulation test dec 1st, implantation bleeding the 7th and my BFP the 14th. She said I would have conceived the 8th but I don’t know how I would have gotten a BFP 6 days later when it would have needed that time to travel down and implant. She kept moving the wand but couldn’t get the angles to change. And my baby and placenta look pretty squished. But I don’t understand this other thing is in my sonogram picture could it be a twin in a weird position? I wish I wasn’t a coward when it come to doctor but I always get nervous about asking a stupid question since they are the doctor. The blue arrow is my baby it had a heartbeat of 161, she didn’t play it for me only told me what it measured. But the red arrow looks strange to me like it could be another sac and baby.

Has this ever happened to anyone?