basic 30 day subscription service only allows 1 character per server to a maximum of 8, unless you pay for one of the other options, you default to the basic service, 1 character per server, maximum of 8 characters. 6 months pre-paid get's 8 per server with a maximum of 40 in total.

I'd guess that the time included with the game purchase is 'basic' service and you're limited to 1 character, this limitation will disappear if/when you subscribe with an appropriate option.