What to do?

Then reroll it, if he doesn't want it.

give him a few days, otherwise go to support and ask for reroll

Send him an email saying that he needs to accept your friend request to get his free game. He might've not paid attention and thought it was just a random request from some random guy.

try to conntact him on his email

Send him an email like this:

Dear X,
My name is Undugu and I am from Africa. I come from a small village so please accept my Steam invite so that I may give you a game you won on SG.

email it to him.

Thank you all :)