Mostly, I think if you think of yourself as strong and athletic, that helps. You are doing things that a lot of "skinny" people can't do. Think of what you are doing for your health.
It's hard to keep a balance with this. Right before I started cycling, I was burned out on aerobics and sort of resigned to middle aged spread. But, I still thought of myself as athletic, as in my former self. Then, when my husband got me out on a bike, I could barely breathe and I wasn't too happy about the way I looked in the cycling apparel he bought me. That was my incentive to start cycling. It was a wake up call.
Veronica is right. We are all built a certain way and at least for me, no matter how much exercise I do, some things are not going to change. And, I would really like it if I were at least 4 inches taller...