What a cute sweater! I don't have an answer for you, but the next time you make a sweater you might want to consider purchasing this booklet:
You can actually custom-make the sweater to fit your dog! The sizes aren't just small, medium and large, but start at size 1 (9" chest measurement) and go all the way up to size 12 (30" chest measurement) so it seems to me it would be more of a custom-fit for your dog. You measure around the neck and behind the front legs to determine the dog's size. The pattern has a corresponding size chart next to it, so when you come to a blank which is usually a cast on, increase or decrease, you just look directly to the right hand side, find your dogs size and fill in the blanks. It's really easy. I just got done making the red one for my daughter's schnauzer. I've only made one dog sweater in my lifetime so I'm not an expert, but just really enjoyed working out of this book.
Good luck on the sweater,