Won a Game 2 Months Ago, Then Obtained Another Key for the Game

As long as you activated the game and didn't win it twice your fine.

edit: to clarify if you want to make a giveaway go ahead

You can give away games that you've previously won.

A mod says it's ok: https://www.steamgifts.com/discussion/YgPxh/regifting-question-ga-inside#7ZaSC2f

Notify the gifter at least 3 times then if no response, wait until 7 days are over and indicate "not received"

Totally ok to do so! I do it sometimes to give back to the SG community