Look more carefully at the picture, see where everything goes and how it goes. Copying other pictures is a good technique for building up to drawing your own pictures well. I find that drawing rough shapes of where everything is and making sure it's all in perspective and in the right place helps. Then when you fill in the detail it's all in proportion. If you start drawing detail with no idea of where it's going you end up with a mess.

To be honest, I'd erase the chest and right arm (her right), the neck's in the wrong place and you need to correct that. The left shoulder and arm look good however as does the right hand.

You're right about the boob line.