It was a show where a guys played a card game and eventually entered a world where said card game allowed you to turn into your cards and battle other players. I can't remember much besides small details like an area where the main characters would relax and get food watching other matches
I'm pretty sure this is Chaotic.
Chaotic tells the tale of a teenage boy named Tom and his friend Kaz. They both play the Chaotic Trading Card/Online Game. Kaz always tries to tell Tom about a secret code to play for real which Tom refuses to believe. While playing online Tom receives the special password. When he enters the password into his game scanner he is transported to a place called Chaotic that is able to take him to another world where the characters, locations and items in the card game came to life.
There are two parts to the Chaotic world, Chaotic itself and Perim. Chaotic is where the people play an advanced version of the card/online game where they transform into the creatures. The games can be watched via monitor by other players.
The second part is Perim. In Perim the creatures, locations and items from the game are real. Players from the Chaotic game can teleport into Perim and scan the locations, creatures and items with their scanners, gaining the ability to use them in their game.
As you can see, it includes both changing into your cards, and a waiting area where the games can be watched by other players, where you you can eat and such and have other teen-related hijinks: