If you're on a directional board like that, my first advice is to never try to center yourself on the board. Keep the setback even when you widen your stance. This means you move your bindings out in equal parts front/back. Trying to center yourself on a directional board will mess up the feel and you'll likely have problems riding.
You ride the same angles that I do. I am 5'9 and have a 23.5" stance just to give you an idea of how narrow your stance is. You should widen your stance little by little until you find the most comfortable. Having a wider stance will help with stability, but you will sacrifice a little control so it's going to feel awkward at first. Once you're used to it, you'll get the control back.
Also, canted footbeds in bindings helps with the knees so that's something to consider on your next pair. Ideally, you want to be at least shoulder length apart at the feet.