Fleeing Wife: Mr Grayson's Beloved

The female protagonist, who just graduated from college, takes her mother's place working the night shift and unexpectedly ends up in bed with a man! Unexpectedly, she learns during a job interview for an assistant to the president that the man she slept with that night is the president himself! To make matters worse, she finds out she is pregnant with his child from that one night and, scared, she flees overnight.