If you use an Apple Watch paired with your iPhone, GPS distances on Apple Watch are based on the actual location of the iPhone to which it's paired. Make sure that both devices are within a 10-yard range to avoid pairing disruption.
However, you can use the internal GPS of your watch. All you need to do is turning the Bluetooth 'Off' - after starting the round on the iPhone - and the watch will use its own GPS showing you distances to the Front, Center, and Back of the Green. Note that you will need to turn off the Bluetooth directly on the iPhone Settings, otherwise the watch will keep fetching the iPhone's GPS.
At the end of the round, turn the Bluetooth ON again to reestablish the connection between both devices. Given that the Watch will not be connected to your iPhone, please note that if you decide to input scores via the Watch they will not be synced to your phone. Make sure that your Apple Watch is charged fully before going out to play.
DISCLAIMER: Unfortunately, Apple still doesn't support standalone GPS apps, therefore you always have to start everything on the iPhone first. As soon as this is available on the platform, we'll be happy to develop another solution.