Your midwife should be able to tell the difference between the heartbeat and the cord. The heartbeat sounds like a horse galloping and the cord is more of a wosh wosh sound. In theory the best place to find the babies heartbeat is near the anterior shoulder however it is possable to hear it in other places. If your baby was hiding behind your placenta it may have been easier to hear the heartbeat higher than you expect. One little trick you could try to decide if that little round lump is a head or a bum is:-
Hold the bump between your thumb and finger. Put your other hand on your baby’s body. Now move the bump back and forth. If it is a head the body will not move if it is a bum the body will move