If I'm 20 weeks and the doctor measured my uterus as 22 CM when it should be 20 CM does this mean that my dates are wrong?
No. As long as you measure within 3 cm compared to your dates, this will be normal.
No necessarily. Us is better for dating than the measuring tape.
No. Uterine size measurements should be roughly the same as how many weeks you are. They can vary by 2 to 3 centimeters. They can vary because of mother's weight or slightl differences between how different doctors get the measurement. Two centimeters is really not significant.