I'd say if you don't want your vest to be this open at the front, then you should probably make a size larger than what you want to make or you could always add to the vertical edge at front, by making 2 - 4 rows.
I was at the photo shoot and this model (above left) was a size small (maybe 4 - 6) and it doesn't come together in the front,which is the way I meant it to be. My daughter, Jamie, at the right is a size extra small (size 1 - 2) and you can see how it comes together even more.
The yarn I used was a Hobby Lobby yarn by Yarn Bee yarns, but you can find a similar yarn just about anywhere. Just look for Super Bulky # 6. Having a yarn with 3 different colors makes it nice to be able to change the ribbon color from brown to olive green or denim blue.
See book this vest pattern is in below. Click on title below front cover to check it out on Amazon.
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