When you applied did you put both names in or just one?
I've had a look at the original image for the reference and to me it quite clearly says 1B 685, so not sure why the GRO can't find it.
ColC gave you the marriage details which I repeat here:-
Name: Sarah Beattie
Gender: Female
Marriage Date: 5 Nov 1860
Marriage Place: Saint Mary Soho,Westminster,London,England
Spouse: John White
You have the exact date and marriage place here. You could contact the Westminster Registry Office and see if they have the marriage in their records.
Email
registeroffice@westminster.gov.uk or call 020 7641 7500.
If they don't have the marriage record then no doubt they could tell you where you can obtain the certificate. Make sure they know that the GRO say they don't have it.