How to fix this caterpie , need some tips & tricks to match the same size ,color, etc

Artwork Works in Progress
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https://bulbapedia.bulbagarden.net/wiki/Caterpie_(Pokémon)

{D3762B22-CD15-4979-9F27-CD32CE164C40}
{D3762B22-CD15-4979-9F27-CD32CE164C40}1912×1079 371 KB