The story I’m looking for started out with the main character either going to University or working in one and one of the teachers or head of departments was working on a time travel device and uses the main character as a test dummy and it allows the main character to go back to when they were young and allow them to rectify the fact that they didn’t come out to their mother about wanting to be a girl. This part of the story takes place in the 1950’s/60’s I think. The mother surprises the kid in that she gave her kid presents as if they were a girl and the kid goes on a journey to become the girl they should have been.