Did you use a thinner yarn than what was called for? It looks like it fits you really well. I love this sweater but am on the curvy side, so the bulky gauge would not work for me.
I used Lamb's Pride Bulky. I went up a needle size to try and get gauge but was still half a stitch over. Somehow I ended up with a skein left? That always seems to happen and I'm not sure why. If you're on Ravelry, you can check out everyone else's projects. Maybe someone switched yarn weight?