Not necessarily for the OP - but in these circumstances, what is needed, is a reissued (and new) etkt number. Then check in with the new carrier/itinerary is simpler. I suspect that the itinerary was ‘booked’ by the call centre/Menzies at Glasgow but the ticket was never reissued to match the new flights, before check in closed at EDI for QR to DOH.
So, with timescales short, never put the phone down without the new ticket being issued. Even if it’s promised that the ‘back office’ are dealing with it.