Hi Julian,
Great news you are up and running.
I'm not sure I understand your concern, what do you mean by
I don't want to be showing up as two aircraft
Do you mean on another PilotAware unit receiving your transmissions ?
If so, this is not an issue, you simply need to ensure you use same ICAO code in PilotAware, as the code allocated to your transponder.
PilotAware will detect the P3I and ADS-B transmission, and recognise that the ICAO code is the same, and provide only one representation to the Navigation Software.
In fact internally it uses information from both data streams, so if for example you have allocated a GroupID in your PilotAware settings, this is recognised by all other PilotAware units, even though internally it may be using your ADS-B or P3I data.
Thx
Lee