Hard to tell much from the angles. In the first pic, you are ducking and way too close to your horse's neck. In XC, you want to be in a more classic shoulder/hip/heel aligned position. Sticking yourself out there like that will eventually result in black eyes and a broken nose.
I should add, ironcially that second pic is more where you want to be. It's hard to explain, but you want to get left behind to some extent but still be in balance and stride with your horse. Hopefully some of the more experienced eventers will weigh in. Looks like you were having fun. I can't wait for it to warm up so I can get outside with my goofball.
I would say sit up straighter, just a tad so your core isnt completely collapsed, That gives advantage of balance if anything was to go wrong, You still want to get off the horses back but it doesnt have to be as streamline as SJ. So your not leaning on your horses neck. You need to give a bit more realese, it comes with practise and once you get the flow of it a bit more. In the first pic your legs look like they slid backwards which is a very common problem, this would also lead to your core collapseing too. If legs go back body goes foward - which isnt good at a gallop over solid jumps. Keep them by the girth, they are the key, that's at the end of the day holding on with. All in all im glad your doing XC!! :)
This is a pic so you can kinda get what im talking about: