Centre 3 boxes

Hi
I have 3 boxes on the homepage using 8.9 stable. I have used the builder to get a row showing 3 objects using the 3 column layout. However they are not center to the page (please see s/shot). I have played about with the margin settings for the row however it does not do it properly (a white border appears on the right hand side).

Can anyone tell me how to centre these?

Thanks
Peter