fraternal twins

goodday twin mothers i would like to know if the same thing happened to you....when i was 16weeks pregnant for the gender reveal scan the doctor showed us the smaller twin is the boy the other twin didnt wanna show gender so we went for another scan about two weeks ago and then the doctor said the boy is now bigger and then he said that the other twin is a girl so im just a bit confused how can the smaller one be the bigger one now😕😐