Diy Coat 3

Place the belt with the right hand edge almost level with the jacket edge on the right.

Then stitch it to the jacket at the centre line. Stitch two rows 1 inch apart as shown above.

Finally the two flaps can be folded around your Scotty's neck for the correct size, then stitched together. 
You can also use Velcro here instead of a permanent stitch to allow for future growth. 
I have found that stitching is fine on a dog 12 months old or more.