...I can almost understand your situation. My bio class is highly competitive too, and it's true that losing a mark can be frustrating. Having a teacher that you disagree with also isn't great. But it might help to touch up on the understanding of the SS scaling system - know that what matters isn't your score, but your ranking - and if there's that many people having almost a perfect score already, then your school's doing something wrong (so even if you have a super high internal SAC it'll be brought down anyway - it's not a comforting thought, but it's likely to happen. Also that if that many people are getting similar marks to you in your sacs, there's not going to be much of a different in the exam either.).
I really don't want to sound annoying, but do you expect something to happen if you whine to your head of psych? In fact it's likely they've already seen it - sacs are always cross-marked, so it's not as if your teacher was the only person stopping you from getting that mark. Multiple teachers would have had to agree on how to fairly mark the sac. Saying 'but that's not fair, it wasn't on the powerpoint!!1!!' doesn't make them more inclined to give you an extra mark either. A sample answer is a sample answer, but you really can't expect it to be the only way to mark things. Even in sample answers given in the official VCAA reports, they say that answers may vary. You can't just copy stuff word for word and expect a perfect score. And if your head of psychology themself said that you had to lose that mark....you probably did have to lose that mark. Sorry.
Look, I get that it's frustrating. My own bio teacher also slips up from time to time, but it's a bit like an echo chamber - if you only use and trust the resources given to you, you won't actually know what's true or not, especially for more important things like the actual exam. Expand your bubble a bit. And you said yourself, that you were 'genuinely content' with your score. Don't let that one mark that probably won't even affect your SS in the long run ruin your life.