By whom? If it was your teacher, shame on them for living in the past. Unless you were in 6th grade sometime before the 70s.
Give it up. Stop doing it. If you ever have to submit something to a graphics professional, they’ll hate your double spaces. I have only “find and replace” to thank for all the people who like to give double spaced copy to me. When you use double-spaces in some graphics software, it has to put that space somewhere. If it’s at the end of a line, a lot of times that second (unneccessary) space ends up at the beginning of the next line.