A joke that went to far

So I was playing with my boyfriend and I told him I was pregnant which was a lie and he got upset and left the house and didn't come back til 3 in the morning. Which I knew he went to his brothers house to have a drink with him but anyways he told me in the beginning of our relationship he doesn't like to be lied to and I really wasn't thinking when I told the joke. He told me that I have to make up for what I did and I know his not talking about sex so how would I make it up to him???