It doesn't look like a twin. If you had another implanted egg it should be in the darker part near the top. Another thing to consider is that since you are so early along the egg could theoretically still split into two separate fetus'. Good Luck!
I'm not a sonographer or anything, so don't take my word on it. But it doesn't look that way to me. I think that there would be more fluid and it would look more like baby 1. Also, how would it implant way deep in the tissue like that? It just seems unlikely to me. But like I said, I could be wrong.
Well my ultrasound pic looked like this at 6 weeks and the other image your talking about is probally your ovary.
I'm not sure in answer to your question....
I do think that you should remove the post & re-scan without your name & what clinic it was at. Can't be too safe these days. Wish I had an answer for you.... sorry.