Only if the low oil warning pressure light came on then it would be a worry. As with tapping/knocking noises.
Unless you were on the motorway at 6k rpm for those 3hrs I wouldn't worry

To check for engine damage, the quickest method would be to assess the top end - remove the rocker cover - remove one cam cap at random
only on the inlet and exhaust and check for scoring marks.
The garage seemed to rectify the problem correctly but I would get them somehow to document what has happened for your records. Try asking for a 2nd repair invoice clearly explaining exactly what happened, the parts replaced etc therefore you would be covered if in the very unlikely event something oil related fails.