Ed wrote

I've just had my kitchen fitted. It looks good but
the sink is off centre of the cabinet by about 1 cm.

Sideways or front to back ?

Is there anything I can do?

Make the supplier do it properly before paying them.

Is there any wriggle room

Not that much usually.

or would I have to buy a wider sink

Unlikely to be available.

and get that fitted?

Get the supplier to do it again, properly.