I love the look of your rock as well. Is that a single rock on the left or a stack of lots of pieces?
IMO your main problem is the rocks are not big enough nor high enough. You said you used the smaller ones. I'd be trying some larger ones as well.
Generally you should be trying to get your highest point somewhere around 2/3 of the way up the tank. At the moment it looks as though you aren't even getting half way. One reason is when you plant it the rocks will soon be covered in plant and you won't see them any more. I was talking to a guy who does aquascaping for a living and he told me he always puts his rocks on other rocks or such so they are higher than the substrate. This way when you grow a carpet you don't loose the rock formation you spent ages getting to look good. It's easier said than done though, rocks are easier to put in the substrate than on other rocks.
My advice is to look at lots of other scapes and see what you like about them and try to do similar with yours. In Iwagumi you have one main rock and all the other rocks have to be subservient to it. As in the others have to compliment it. The main rock should be bigger than the rest and placed first, then work from there.
Another thing you may want to consider is that in nature rocks like this generally all lay the same direction. As in all the lines will be on the same angle. See how they are horizontal on the left rocks and not on the right?
I like the left and Don't like the right. It's boring. I'm being blunt, not to put you down but because I know you can do better and you'll be happier when you do.
If it were me i'd be trying to add a bit of drama to the scape by having the rocks on an angle instead of flat.
Have another go and don't be afraid to use bigger rocks. If you can arrange them in a box the same size as your tank with most of the front cut out and substrate in the bottom, that way you can quickly change things and not worry about breaking glass etc.