You're not doing anything wrong — that's on the interface, not you. Right now these challenges check your answer by scanning the whole code, which makes it genuinely unclear where things should go. I'm reworking them to use clear, labeled input boxes (one per answer) so it's obvious — coming in an update.
For now, "Hex & Memory" just needs these three values to appear anywhere in the code: 0xFF, 255, 65 (binary 11111111 → 0xFF, 0xFF → 255, 0x41 → 65). Thanks for the patience.