Sonny looks nice and relaxed, you look quiet and confident, good job!
You are riding chair seat a bit. Stand in your stirrups and really get you feet under you, then sit down straight down. Get used to what it feels like--one thing I do is just randomly stand in my stirrups when I think that my butt is going back and my feet are going forward, then sit back down to get back in position. You need to develop a centered seat.
One way to think of it is this--if your horse shot forward suddenly, would you land on your feet or your butt? With a centered seat, you'll probably stay with him better--you need to put your center of gravity right on top of his...whatever you call it at his girth--the place he spins around, I guess that's his center of gravity, too. Think of the area from your belly button through the top of your thighs as welded to the place you girth him up--that part of you and that part of him are all one piece. When you balance right there, you can stay with the horse wherever he goes because you're always right there with him.
When you ride with a chair seat, you are behind his center of gravity, and you're more likely to hit the dirt right on your butt if something goes wrong.
Don't know if I explained that well...
You both look good for your first time in the ring, though!