l have had to repot my coprosma shrub and the big roots broke

Hi Patsy and welcome to GoY. What size is your Coprosma?

It's about 3 feet high and quite broad. It has plenty of the smaller roots intact.

Well, as my father-in-law would have said, 'it's got two chances'... All you can really do is wait and see and keep it well watered.

Also, selectively remove about 1/4 to 1/3 of the foliage, to slow evaporation, and allow the remaining roots catch up.