I can't rotate walls when building

I must be missing something really simple, but it's driving me out of my mind. I'm only able to place walls to the left and right of the grid. I can't seem to rotate the wall 90 degrees so that I can then place them on the front and back, if that makes sense. I've tried Z, Y, and X, the walls will not rotate for me. I've searched, and I can't find what step I'm missing.

Edit- I finally found it, I feel so dumb. All I needed to do was tap the Z key, not try to hold down and rotate it. *headdesk*
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