can I see your layers

[white reef]

if you select both the image and the mask it is clipped to and do ctrl+e, you should get a flattened layer containing only the area you want to print

[teal bough]

that's it, really great.

thank you so much

[white reef]

now you can copy paste it to your A4 document

but make sure it is pasted in full resolution

[teal bough]

can i replace the original photo by a single function in all layers, or "simply" build it from scratch?

[white reef]

I can see you used a smart object as your photo, if the next instances of it are copies then you can easily swap it inside the smart object