Pull the ends through that elongate the scarf in front. I think it helps like a v-neck compares to a crew neck sweater.
I am also chubby with a round face and this is what I do. As long as you don't tie it right up under your chin it actually elongates your face and neck. I am also big busted and I feel like the ends of the scarf hanging down kind of hide that area. I don't buy thick, bunchy scarves. All of mine are made of thin material.
Good luck, a scarf can really pull an outfit together!