Hi Karen,
Not sure if you got this resolved already, but if not: (Also, sorry for the wall of text

)
From what I can tell BF leadership keeps a list of eGO Platoons near the bottom of the following sticky thread found in the BF Division Forum:
Battlefield Leadership/Server IP And Rules
Looks like you were trying to join the third one, C Platoon.
When applying, you'll want to put your forum name and rank, since I'm guessing non-members frequently apply for the platoon and it would cause confusion with how one becomes a actual eGO member and not just a platoon member ; That or message one of leadership directly via Forum PM, TeamSpeak, or Origin/Battlelog. That'll let leadership know who you are and that you are a member wanting to join one of the platoons.
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Alternatively, and correct me if I'm wrong anyone, you don't necessarily need to join a platoon to add the rank.
Since joining one of the platoons usually forces your tag to the full eGO and not 'e' or 'eG', I made a guide which was stickied in the BF Division Forum on how to do it manually.
Here's a link to the guide:
How to add your "e" tag in Battlelog [BF4]
Hope this helps!
Feel free to post back if you have any questions, comments or issues.