Hello,
Welcome to the ehealthforum and I am really glad to help you out. Since you had your periods on 16th March, so it is most likely the first trimester of your pregnancy. You must have seen other structures on ultrasound which you are confusing with the baby as during the first trimester only organogenesis occurs and development of the fetus occurs in second and third trimester. However you must get regular ultrasounds done to keep track of the fetal growth.
I sincerely hope this helps. Take care.