120V Receptacle wiring

[Doityourself]

Hi all,

I need help in wiring a receptacle with 120 V for the patio from the main power box with 240V originally coming from the two Black conductors in the wall, and a barbed neutral copper.

I have wired the neutral and one black conductor on to the receptacle to get 120V, what concerned me was where to ground the receptacle while the neutral conductor from the wall has now been wired to one of the receptacle terminal?

Your help is appreciated.

thanks