No worries! It can take up to 24 hours for an egg to be fertilized. From there the embryo needs about a week to work from the ovary through the fallopian tube and get to the uterus.
The term thagomizer was coined by Gary Larson in humor, in a 1982 Far Side comic, in which a group of cavemen in a faux-modern lecture hall are taught by their caveman professor that the spikes on a stegosaur's tail are so named after the late Thag Simmons.
Thagomizer has since been adopted as an informal anatomical term, appearing, for example, on the website of the Smithsonian Institution. The term has been used in displays at Dinosaur National Monument in Utah, in the book The Complete Dinosaur, and in the stegosaur display at the Smithsonian Institution.