You probably hit it just behind the liver and ahead of the stomach. The reason I say this it because I shot a doe on Sunday and it had fat all over it as well. I shot it just behind the liver and it exited just behind the heart on the other side. It went about 300 to 400 yards. The blood trail was not very easy to follow in the beginning but after about 200 yards it got a little easier. When ever we found her she was still alive. I had to finish her off with a knife to the heart. She was a huge doe. So you possibly could have hit it in this area.