A buyer cannot cancel an order.
It is likely that you accidentally clicked more than once on the Buy button, especially because sometimes the screens are slow to react.
NOW.
Contact the seller. Explain that you only wanted one not three. Ask that he cancel two of the purchases. If he sends you a Mutual Cancellation, agree promptly. Leave positive feedback.
If you have language problems and I think English is not your first language, use GoogleTranslate to change your exclamation from your first language to English.
Actually you can also change it from your language to Chinese/Cantonese, since that is the other official language in Hong Kong.