Okay. Just before, she tells him that the semen from their love-making the night before, is leaking out of her vagina. He asks if he needs to "top her off", which is a phrase used when filling up a container, like a gas tank. He's asking if he needs to put more semen in her vagina to replace what leaked out. He's asking if they need to have sex again.
Please note, most women do not like having their vagina referred to as a container that needs to be filled. He only said it because they had so much sex that common sense left both of them.
It's just them being spaced out. There's no way of knowing if the semen fertilized the egg or not until a few weeks later. Only then, would it read on a pregnancy test. Sometimes people get pregnant after one time, sometimes it takes years of unprotected sex. Everyone's different. That's why people should use condoms or other contraceptives until they're ready to have a child.
"Need me to top you off?"