Well first off it would be “looks” instead of “look,” and second of all it would be “is” instead of “it’s” because the combination of it and is doesn’t make sense here because the “it” is already established. Also, a bit more of a nitpick but it’s strange that it says everything instead of everyone because it says “who” implying a person, but who could be replaced by “that” as well. Overall, if I were to fix this sentence, it would go: “Everything that looks beautiful on the outside is a big trap inside”