I am afraid I fucked up my perfect relationship

Katie
So I thought that it would be funny to play a little prank on my boyfriend (who is my best friend and the love of my life. We live together, we work next to watch other, we do everything together.) Anyway I thought it would be funny to put him on and tell him I am late and to let him think I am pregnant. So I told him when we woke up that I am late and obviously he has scared and I am a really good actress so I played along with it. We went the whole day and when we got home I started to milk it again and told him that i wasn't late but that I was actually pregnant. And after a little while I finally admitted to him that it was all a joke and that I am not pregnant at all. 
Well he didn't take to well to that. He was extremely hurt and I had no idea that it would have this kind of effect on him because if I did of course I never would have said anything. I didn't even do it for a good reason. It's not like I was testing him or anything... I just wanted to see how he would react. But now he is upset with me. He didn't yell or get super angry he was just very hurt and depressed and confused as to why I would do something like that to him. And it wasn't until he asked me did I realize that I didn't even have a good reason. 
Anyway I hate this feeling of hurting him. I have this lump in my stomach all day and I need to make it better. I have told him I am sorry and asked for his forgiveness but he says he still needs time. This worries me because he is my best friend and I don't want to lose him. He said I won't lose him over this but I want to make it up to him still. Anybody know what I should do or say? We are like the power couple, all couples around us want to be like us. Then I go and do this stupid shit... It was just a stupid prank that went horribly wrong.