Access to Qantas Club lounges for Club members with no status is conditional on travelling on a QF, BA or JQ flight number.
A QC member flying on other OW carriers does not get access.
If you had OW Sapphire or Emerald status, you would have been able to access the QC lounge.
More information
here (see the following note under the Qantas Club and Frequent Flyers table - " + Must be travelling on a Qantas, British Airways or Jetstar flight number.")
And welcome to AFF