That’s rather difficult… I’ve always been of the mindset that the past has happened and there is no need to look back at mistakes. Just look forward and keep on marching with new knowledge in your arsenal.
But, for the sake of the question I would say I would change my past obsession with games. I grew up fairly lonely and independent. I learned to attach to games to kill time and kind of throw my mind out of the loop for awhile. I have since grown out of it, but games definitely affected my school career.