To add to the above, extend the template so that it sticks out a good 10cm or more in front of the body (i.e. in the area the neck would be when fitted). So you end up with a long neck pocket slot in the template. This allows you to keep your router level when cutting the front of the pocket. If you have it flush with or only just extending over the body, the router can tilt forwards a bit if you are not very careful.