Sounds like you are doing well so far. I can relate to the worrying, I have an 11 yo daughter and have worried that she will have a hard time at school. She has just started secondary school and come out to her friends and it all seems to be going ok so far. It's true that one of the things mums do best is worry, we can't help it. But the most important thing your son can have is your love and acceptance, with that secure he will do well.
I told my mother about a month ago about my sexuality (and not my gender) and she was fine with it. I think that you shouldn't go on about it to him. If you like you could ask him if he wants some sort of support.