The female reproductive organs are actually quite small, they take up very little space at all unless there’s a baby in them, and clearly we can see what happens then. Your heart is on the order of 300-400 cubic centimeters for example, while the uterus is usually about 50-100 depending on certain factors. Ovaries are like 6-7 cubic centimeters each. The vagina is collapsed unless occupied, so takes very little space as well.

Men have a couple of replacement pieces (like the seminal vesicles) but they’re tiny.

The vast majority of that area in both genders is taken up by things like the bladder, parts of the colon and rectum, muscles, and fat.