The  shape looked like this, next I added inserts

It feels like designing something out of Meccano.
Maybe somewhere in my subconscious, that is why I added so many holes.
One thing I noticed was that fewer holes meant a quicker print time.

Then the joining piece was added. It seemed slightly wonky but still pretty sturdy.
I checked and it fits the gully around the centre of the display, with the exception of the flat cable that goes to the side of the display. There appears to be a slight twist that became more pronounced after a day or two.

Now I have to decide if it will be a face on wall mount or an angled desk mount and then figure a way to attach to the screen and also support the Pi.

Here is a picture of the wires needed to plug in the touch screen to the Pi.
These wires are so fragile and bulky,  I am afraid that one of them will pull out.