I think you look great for your first time! Great job, and welcome to the dark side. Mwahahahaha......
Anyway, here are my few bits of advice, mostly just reiterating what others said.
Many new riders think of posting as an up and down motion. Really, it's more of a forward and back motion. Let the horse do the work to push you out of the saddle; your job is staying balanced and out of her way.
Also, like someone else said, you don't have to be so folded over in two-point. It's more about being out of the saddle but still balanced over your legs.
When you feel comfortable, try taking off your stirrups and working without them, especially in the rising trot. It is very hard at first, but it will help you "feel" your horse's movement and will make your posting a lot more subtle and effortless when you put the irons back on.