Absolutely unhappy with the new plaster, doesn't fit - please give tips

…give the unconventional laying pattern a chance.

Wild bond of three formats :-)

Often new things look unnatural and strange among old things. However, this changes, for example, through habituation.
In half a year, the pavement will have also adapted somewhat. Once it has weathered, everything is a bit more neutral.

This pavement will probably become grayer and lighter over time, won’t it?

Concrete pavement does not age particularly well. Especially nuanced concrete pavement often loses its nuance and approaches standard gray. It’s not exactly what you want to hear after newly laying it, but the pavement certainly won’t stand out as brand new after a few years.

The contrasts will diminish somewhat and fade. Overall, it will become lighter, the dark color does not persist, and it will be more homogeneous.

it looks pretty impossible

It looks good though. You can hardly even notice the cross joint.

The palisades in the emerging gravel garden harmonize very nicely with the roof vents. I find the small-scale cobblestones / granite blocks from the neighbor appealing. Yours wouldn't stand out as much and also wouldn't be bland.