If you donate or sell your eggs, does that mean someone else has your baby or babies?

No and not selling! You may donate your eggs but you're not selling them, in the us (but not in canada and some of europe) you may be reimbursed for your time, discomfort, travel, taking shots etc. But we are not paying you for your eggs any more than you should be selling a kidney. You are giving another couple ("the intended parents") a gift of great value: the chance to be parents, but it's their babies not yours.
Perspective. Some people, donors and recipients have difficulty with gamete (egg or sperm donation) because they consider the egg or sperm to be their child. However, the egg or sperm is only half of a potential baby. Most eggs and sperm never become babies (consider that there are 7 mill eggs and hundreds of millions of sperm). Only you can decide how to perceive the gametes - not one answer for all.