I see you offset the bow on the tree, I assume to line up where your arrow rest and nocking point will be. However at this stage I would still center on the tree. Another thing that will help you out, is to level the tree and your bow. Place the level across the back of the grip area. If you're trying to use the lines on the siding, check to see if they are level as well, as this will fool your eye. I agree with big country about the tillering gizmo, just a 6" piece of wood with a hole in the center for a pencil. Run it along the belly and scrape the pencil marks away. Good luck with the rest of the build.