Extra piece of placenta

Has anyone ever had an abnormal placenta? I believe my Dr called it a "sag". I had my scan last week and was told I have a extra piece of placenta. Its not harming the baby at all. He is growing sorta big in the 87 percentile at 21 weeks though. I wish my doctor wasn't so rush rush because I'd like to know if it could have been twins at one point. Has anyone had this and went full term? Thanks loves!