Prof,
You have a very nice, well balanced design. You can just take your time and execute it. You can also tweek it a little, the choice is yours.
Your design will never look exactly like the original rifle because the overall proportions of the butt of your rifle are somewhat different than those in the photo in the book. That is not necessarily a bad thing; but it is the starting point for your carving. Your "canvas" is a different shape so your creation must also have a different shape. Note that the lower edge of the cheek piece in the Fordney rifle extends a little further down from the comb than yours. The position of the lower cheek piece edge controls the shape of the carveing beneath it. You can't move the lower edge on your rifle - and aesthetically it looks fine the way it is.
You can redraw some of your carving with an eye to extending it along the length of the butt a little. But remember, a little will go a long way. If you leave just a little bit of additional space between the arcs at the end of the volutes and thicken the arc at the middle you will get a more linear, stretched-out feeling that you get from the original rifle. But keep in mind that the carving is there to fill up a space, a canvas, if you will. Focus on filling up the canvas you have with carving that is "inspired by" the Fordney rifle and you will have a rifle to be very, very proud of.
Best Regards,
JMC