I don't jump cross country, but you and your horse look great! The saddle doesn't look to big to me! The only thing that I could critique is you just need to release a little more! I have that problem but I've gotten better! Like I said im a jumper and I have not ridden cross country, but that's all that is see that needs a little fix! Good luck!
I worry that the horse may have a little more contact than he might need (that he "pulled" you over the jump with his mouth). However, it is hard to know how much you had to hold a bold horse back here.
As for the lower leg, I agree you need to rotate your lower leg to allow your foot to go more along the sides of the horse and point forward. This is important for two reasons.
#1. Although you don't feel the need to use spurs on this horse, you may, sometime in the future, need to use them on a horse. You are learning to ride off the back of your leg. This is a hard habit to break.
#2. You are riding XC. Sometime, if you go to the higher levels, you may be jumping VERY narrow fences and corners. These jumps usually have light, very breakable poles for the flags. However, some have very strong vertical elements. If you hook a toe that is sticking out, it can pull your foot around backwards. That can equal time in a big cast.
Learn to ride with toes forward....always. If you need to turn your toe out to engage spur or a stronger leg, turn it out, use it, and turn it back forward.