That sounds small as GCCs are typically quite active and playful. Also need room to fit all those toys and stuff. But like above said, it could be okay if the bird can come and go on his own for many hours each day and is closed up for bed. Do you think your bird likes the cage? Maybe reading his behavior can help because if he is really active and spends a lot of time in the cage then he deserves a bigger one, right?
I've found great cages on craigslist or Facebook marketplace. Recently got a great deal on a flight cage from chewy.com as well.