Am I doing this right?
I'm going to put playwood for more support.
I'd appreciate your advices.

 

Welcome to the forums!

You lack nailing surfaces in the inside corner on the back wall with which to attach your cement backer board and your drywall. A stud should go all the way up the wall to the top plate on either side of the 2x4 of the half wall. You may even want to run one on the flat between them to make a "U" shape.

Include a little more detail about the rest of the shower - type of pan or drain system? Walls to be tile? Include a picture from further back so we can see the whole build.

Why is there electrical running in a 1/2 wall of a shower?

 

A 2 X 6 or 8 sitting flat in the joist bay from bottom to top plate would have given you the nailers and support the knee wall.
What's the horizontal 2 X 4 in the knee wall for?
Those studs are 16" or less on center, right?

 

What Z said. Not being too critical, but you will tire of that small wash box of a shower if that is it. Hardly space to turn around, then you will be adding 1/2" cbu and tile to it. Really small. Any way to make it more reasonably sized while you have it in the pre stage?