Or you can just try to sell it on the Digital goods section of this forum, there are a lot of people who are constantly buying this kind of goods, if it is a good one, then you would be able to sell it quickly, otherwise you will have it on your portfolio forever
good luck with that mate, i am sure that you will find a buyer as soon as possible.
G2A is not a low fee, plus the fact that that entire site is full of frauds and all that. I'd try to avoid G2A at all costs, if possible of course.
If you want to sell the game for Bitcoin, try to sell it on here. Advertise it in your sig and post it in the digital goods section, you're going to limit the amount of risk you're taking as you're not using a shady marketplace (G2A) and you're going to be able to handle EVERYTHING with regard to the money you're being paid.
Goodluck on selling it BTW!