Some help figuring this out please

I was showing a lady I work with my 7wk ultrasound the other day. She pointed out something in the upper left corner and asked if I was sure there was just one, because it looked like another babys bum in the corner that just wasnt focused on in the pictures. I told her "nope, just one from what the nurse practitioner and Dr said".

Now that she pointed it out, my eyes keep going to it...it kind of does look like a baby's bum lol. I trust my Dr and her assurance that there's only one, and know it's not another baby, but now I'm curious as to what it really is. Any thoughts?