You'll have difficulties with the manzanita no matter how you arrange it because the branches are too thin compared to the size of the gravel granules. It's a losing battle for the twigs unless you replace it with wood that is much larger.
you could get a few slightly bigger rocks, make a kind of pile of them in a corner and have the branch inserted into them and sticking out? making it raised might look better as the plants in the back are overshadowing it
Yep as everyone has pointed out the scale of the tank is thrown off by the larger granule size. When working with smaller tanks you have to take into account the scale of everything more. Its easier with darker substrate as it would blend together more but the ones you have are all different colors so its really noticable how large they are. You can do what solcielo said and use sand as that would give it a much better look and is easy to do!