Pen tool is cutting off my image

Hi, I am new to illustrator and am taking a class online. No one really responds to the class anymore and I don't want to wait and see if I get a response. I was wondering if someone could help me here. I am learning the pen tool and how to use it we are tracing an image of a cat. Below is how is started tracing the image but when I get to the nose part and try to make a curve, it is cutting off the orginal image and is making a whole new image. How do I get this to stop? In the video from the class it wasn't discussed and I would really like to know how to fix this. If you need more clarification please let me know.