No, it isn't just you. The orange arena is full, the players are politely being told to go to other arenas.
Or as the help (game info/arenas) says,
The Aces High arenas use a dynamic or floating limit for the arenas where there are two, or more, of the same type. For instance, the two Late War arenas will show a limit that changes as the amount of players in these two arenas change.
The arena limits are governed as follows: As an example, if the Orange arena reaches a certain percentage of its maximum capacity, the server will adjust the Blue arena limit to a higher number. When the Blue arena reaches a certain percentage of its limit, then the Orange arena limit is raised. Conversely, the arena limits are also reduced in the same manner.
This gives the possibility of an arena limit being lower than the actual current number of players in that arena.
