Here's my critic.
Please refer to upper pic...
(1) The placement of the larger piece of wood should be between the 2 smaller ones. Also, because of the form of the side facing the front (circled), you will end up with an ugly space there as planting around that space is akward. Try to let the side facing the front have more texture and is easier to plant around.
Wood(2) and wood(3) is too similar in shape (elongated), either change the wood or use different angles. Also consider bleaching / lightening the darker piece to balance the hues.
(4) A flat gravel is boring and lifeless. Try to use some angles or bury part of the woods in the gravel to create a more natural look, like a buried driftwood uncovered by currents...
(5) Try to follow the direction of the radial gradient of your background. A U shape is the best.
Please refer to lower pic...
Then grow a carpet around the structure and decorate with Java Fern, some red plants, etc...
The arrows are there to llustrate how this layout can express it's energy by radiating out. Fits the background perfectly.
2 cents!