return or not return

that is the question. does anyone know if you HAVE to show a return ticket when you enter usa? on some website it says you have to. it would suck so much if i have to because i am not going back the same way, to tokyo. my plan was to slide over to nyc and then maybe go back to europe from that side. and i can’t afford a ticket to europe right now… what to do? help me out please! i am also in a hurry.