I think you should put the wood on the left hand side. Lay it down from the position it is in now and prop it at the back with a few rocks that spill out from around and underneath it to the left slightly towards the front left plant.
Then that can be your feature and you can work around it. leave a nice arc of substrata on show in front of the wood but carpert to the left and right and then add a colour feture plant just to the right of the cabomba. Something that is red and grows tall would work or maybe a lilly but I don't know what plants are from where just colours and spacing. The right hand side should then grow nice and bushy and fill most of that space.
The plants at the front to the left or whatever you may change them too just try to get them to be placed slightly further to the right a little so that if you have a rock group they start to grow around them.
Hope that makes sense. I can't use photoshop or paint so will let someone else have a go if they want or could maybe sketch what I have said to see what you think.
Kind Regards,
Adam