If you bought the NX directly from the C-Store, you have only unlocked the ability for all your characters to requisition the ship. Each of your character (if you have more than one character) will still need to go to the "Starship and Shuttle Requisition Officer" in ESD to actually requisition for the starship.
Oh yeah brother, I tried that. I guess my rank isn't high enough? I just started playing. I'm a LT lvl 4.