Hello @dmllewellyn ,
Your watchface will not show up as a sideloaded app until it is built and downloaded.
"Sideloaded" is more an indication of a successful download than it is part of the download process.
You will need to connect the developer bridge on both the watch and your phone. This takes some attention as the watch will tend to disconnect the developer bridge depending on what you do with it.
When you have connected both, they will show up in Fitbit studio under the "Select" menu options
When selected, the next build will target the watch, and phone instead of the simulator.
Hope this helps.
Regards,
Reign