The Sanskrit shloka (verse) that conveys the meaning "you are complete the universe within yourself" is:
त्वया त्वमेव जगतः पूर्णत्वम् (Tvayā tvameva jagataḥ pūrṇatvam)
This can be transliterated as "Tvayā tvameva jagatah purnatvam" and it expresses the idea that you (referring to the addressed person) are the completeness or entirety of the universe within yourself.