I'm playing ruby and I need to win the hyper contest in cuteness and there is a trainer with a magikarp which always wins the first round
The bad news is my skitty won't eat more pokeblocks and its cuteness has reached the pink circle in the chart though but how do I improve or feed it more?
This most likely means that you have maxed out the contest type that the pokeblock corresponds with. My feebas did the same with beauty (blue pokeblocks), which was good. So this may be your "problem."