Your speedo is technically within tollerance, as, by law, speedos are never allowed to under-read, but can over-read by upto 10% - though Audi speedos are generally quite accurate.
For example, at a genuine 60mph, the vehicle speedo can actually (legally) display anything between 60mph to 66 mph.
I think the OP may have something confused with either his maths, or got his words the wrong way round!

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Sean - Independent Motor Vehicle Technician (retired)
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'07 Audi B7 RS4 quattro saloon 4.2 FSI V8 32v (BNS) (with ceramic brakes) - WOW
'06/7 VW A5 Golf Mk5 GTI 5dr 2.0T FSI (BWA) DSG, fully loaded, colour coded,
'98/9 Honda CBR600FX, the blueberry trifle
'03 Audi B6 S4 quattro saloon 4.2 V8 40v (BBK) 6sp manual, fully loaded (gone, but not forgotten)