I like the overall vibe you're going for! The uplifting rhythm and the melody are really nice, and the whistling is a great idea for the theme you're going for, though it is a tad bit off key. If you haven't yet, I think you could try using some quantization to clean up some of the rhythms in there to improve cohesion between your various instrument parts.
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Oh yeah, I totally get that, I'll be working on a piece and think it's perfect, then the next morning I notice so many things my ear had gotten used to and missed. And for the whistling, I really admire the fact you actually recorded it, that's super cool, and you definitely did it way better than I ever could've. You've kinda inspired me to try something like that in the future, and maybe incorporate my own piano playing into a piece.