You'll find it easier to focus if you boost the brightness or gamma heaps. Jupiter will appear as a solid white disc when focused well, and as the focus goes out in either direction, it will both grow, and feather out towards the edges... so the central area of the disc will appear solid whit while the outer area will be progressively darker somewhat like a halo on stars in DSO images.
Once there is no halo around it you can safely assume you are focused
Best of luck with You vs Jupiter, Round 2!