Entering Romania by tourist visa. Do i need return ticket?

Hi this is my first post here. I'm travelling to Bucharest in December but i bought one way ticket. However, i got my tourist visa already but it lasts for 8 days. I already booked a hotel too which the issued me a "voucher" (scanned version). I am Thai citizen, anyway. I'm really not sure if i need to show my return ticket to thailand or not despite the hotel booking voucher. Are the immigration officer serious about this? Some of my friends said that i may not be able to pass the immigration in Thai airport if i dont show my return ticket.
Can it be a confirmation from airline booking agent said "reservation confirmed" ? Kinda worried now coz i planned to buy the return ticket later.

Thank you,
Be