This is really neat. I couldn't do it, but I can see what you're getting at....here are a couple of thoughts.....
The tree at the right corner. Look at the base of it. That looks narrow compared to the rest of the tree. It also looks a different color.
The lower railing by the tree looks off. It's narrower and the right side should be angled down toward the right corner. It looks to be going straight across the picture. You have that top railing angled. The bottom one should be too.
Look at your vertical posts (up/down). The one on the left is taller than the other two.