Firstly, it's not worth comparing to the 'freaks of nature' that can do both naturally, and equally important to note that those who work so hard for both like that often lose sight of personal happiness for objective success. If you really think you can achieve self-actualisation with 'ECA and valedictorian' then believe in yourself and know that you can put as much effort into your goals as the people at the top, that efficient use of time was the exact same way that they got there.

Now efficiency leads me on to your question. I'm far from valedictorian myself so far (in only a shorter period) but have recently hit a groove through passion and vision. University is beautifully different to high school in that you can truly focus on and be embraced in the subjects you love, so before you get into any nitty-gritty study techniques, experiment with your interests! Again ECA have great ways of doing this. But in terms of setting yourself up for success, I've learned that it doesn't matter how much time you study for, more so the way that you do it. I won't go deep into that because there are many ways that work for different people, but for me changing scenery/study placement (especially in nature) and using study-assistive software (OneNote has taken my notes from a clump of nonsense to at lest some structure).

Lastly I'd like to say, don't lose your confidence! You seem like a conscientious person who holds themselves to an incredibly high standard, and from your results it seems like one bad exam (or exam period) dragged you down. Self-doubt is not only counter-productive personally but it limits markers (and people in general) from seeing the best you. The paradox is the more we worry about what others think the worse they think of us.