Does a girl's refusal to marry me after performing Istikhara prayer mean that I am the worst of people or not among the good ones?

A girl's rejection of a suitor does not necessarily indicate his badness; this is a matter of divine decree (qadaa' wa qadar (definition)). The criterion for a person's goodness or badness is his religiosity (deen), piety (taqwa (definition)), and character (khuluq), not whether a girl accepts or rejects him. However, Islamic law (Shari'ah) has made religiosity and character the basis for acceptance or rejection in marriage.