I agree with putting a 3rd rock on the left side to connect the layout.
As the current bigger piece of rock, I think you shouldn't place it parallel to the gravel-line. When view with the upright stemmed plants behind, the whole layout is stiff as it's too perpenticular, same goes for the smaller rock, though it's effect is weaker. Rocks placed at angles will look more natural and prevent too many straight lines of perception.
2ndly, the very clear contrast of 2 totally different types of leaf shapes on both sides is upsetting. Try putting some broad leaf type like those on the right among the left to cohesively blend the layout together.
The gravel is almost white and does not match the blue backdrop, looks artificial. Plant in some foreground plants. Glossostigma is the best as it can balance both sides of the background visually.
Try to shift the red plant more to the left/off-center. When it's redder, it'll look really good.
The right side needs some midground plants.
2 cents!