Airport Express to Hong Kong Same Day Return with Octopus

Hi there, If I use an Octopus card from the Airport to HK Station, then return to the airport on the SAME DAY, but from Kowloon station, do I get charged twice for the trip or would I only pay the HKD100 same-day return fare?

I'm going to be landing in Hong Kong early morning with a connecting flight late that night. Just trying to figure out my best options for transit use. Many thanks,