It looks like a good fit.
You can also measure your horses back with a bendable sturdy wire that holds a shape well. I use a coat hanger. Or you can use soldering wire. (Make sure your horse knows it won't "bite" :) )
Measure at the withers (bend the wire to form an A/arc over the areas) where the front of the saddle would normally sit and down until you get to where a saddle should stop. Each time you measure place the newly shaped wire into the underside of the saddle at the exact points the saddle will rest on your horses back.
If the wire has to be much narrower or wider, the saddle might not be a good fit.
It's a lot like nuts and bolts - if the rider's nuts, the horse bolts! ~Nicholas Evans