Urgent Help Needed

[F1ADO]

I am trying to build a wall of cabinets so that my new Pachinkos will sit flush.

I had the bright idea (not) of building the start of the sub frame directly on to the wall ( thought it would add stability) but now I'm stuck as to what to do to build it out from the wall.

Hopefully after sleep, I will have a brain wave but failing that can anyone steer me as to what I should be doing next.

As you can tell, DIY is defo not my forte.

Thanks in advance.IMG_20201129_005439.jpg