If you want to make a repeating pattern, then some of the objects must extend beyond the edge of the confining rectangle and they must be a copy of the one at the other side in the same position to the rectangle.
The “pattern” you show will never tile properly because the edges don’t match up. I think you realise this
To make it look “organic” you should have lots of elements – the more the better – but none the less the edge elements must repeat.
See the instructions for making patterns.
To avoid an obvious tiled look to a pattern you can then rotate the pattern within the shape by, say, 20°or so.
You can also use a subtle gradient or gradient mesh behind the pattern to camouflage the tiling, in which case the area between the stones in the pattern should be left uncoloured.
I once did a rendering of a sea wall using a pattern of stones.
The client was amazed that the job hadn’t taken longer – he couldn’t understand how I had time to draw all those stones.
He couldn’t see that it was a simple repeat pattern because I had rotated it.
I kept the secret up my sleeve and he paid his bill without even questioning it :-)