Thanks I actually used the up down method with the track saw but from my understanding that’s more about the board edges not being 90° which seems to nut be an issue when i measure it, but the hourglass shape wouldn’t be affected by that right?

Thanks for the tips, i have some extra boards so maybe i can just practice a bit with the jointer and get a better result, the bench plane also seems like a good option. Though I’m still confused why the tracksaw and parallel guide also gave me the hourglass shape. In the past I used that setup on plywood for similarly long cuts with better results…