The belt doesn't seem to get in your way at all. In fact, most of your belted sets look better than your unbelted sets. You tend to lift your chest in the squat and you push the bar forward with your shins in the deadlift setup. I'd fix that. I suspect your weights are not really heavy enough to warrant a belt anyway, so you may want to do without one for a while longer. The much bigger problem is that you are seriously underweight. I would suggest not worrying about a belt, training hard, and eating more.