I was on starboard — how can I still lose the protest?

Having right of way isn't a free pass. Under Rule 14 you must still avoid contact if reasonably possible, and under Rule 16.1 if you change course you must give the other boat room to keep clear. Starboard-tack boats lose protests when they alter course too late or fail to avoid avoidable contact.

<iframe width="560" height="315" src="https://www.youtube.com/embed/mYKJXeCc0fY" title="Sailing Kiwi" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
<p><a href="https://sailing.kiwi.nz/windward-mark/starboard-still-wrong/">Source: Sailing Kiwi</a></p>

Next on this shelf — The Windward Mark