DICE and EA are aware of the fact that there are more players who want to join the CTE than they expected, therefore it´s closed at the moment.
There will be more servers soon, please have a little patience.
Thank you and welcome to AHQ
Best Community in the World
I am a volunteer, I do not work for EA.
Registration will be closed for a short while, due to an unprecedented number of players joining - keep an eye out for news regarding whether it'll be open again and keep trying. You should be able to get into the CTE soon enough.