White border on cover

I'm using Sigil 0.9.4

The book is finished (very nicely too, thanks Sigil people) but the cover has a white border.

The same book created in Calibre doesn't have a white border.

I've edited the preserveAspectRatio to "none meet" which made the cover display a little better but it still has a thin white border.

The cover image is 625x1000

Have I missed the thread that solves this?

Is more information needed?

Thanks in advance.