Here is a speaker who sums herself up through the voices of other people. Every line begins with "I am" or "I am not," but the words that follow sound less like her own opinion and more like things she has been told, or has come to believe others think. Phrases like "the 'leftover'" and "the 'why are you even here?'" are placed in quotation marks, which suggests they are echoes of cruel remarks that have stuck with her.
The speaker feels rejected, unwanted and deeply inadequate. She measures herself against an unnamed "clever one" and "skinny one," and she always comes up short. The list builds like a pile of evidence against herself, ending with the flat, defeated line "I am just not good enough." The word "just" makes it sound like a final verdict she has stopped arguing with.
The mood is bleak and raw. The short, repetitive lines feel heavy, and there is no hope or comfort offered. That bareness is what makes the poem hurt: it lets us hear how negative labels can turn into a person's whole sense of identity.