You look really good for your first time! I know my first time English I didn't look that good. But yes, just a little more release on the rein would be good. Also, when under Western, you do not have to ride with one hand unless you're showing.
Actually, you should only ride with one if the horse knows how to neck rein (Im assuming he does). If not, use two hands. =] But you looked really good. I rode in an English saddle, it was fun, but I ride bareback too, I have been bless with good balance, every horse trainer/rider I talk too always says I have good balance, xD