In order to play on the NA servers you first need to activate that region in your battlenet account the same way you did for activating for SEA (I think). Go to www.battle.net
log in and you'll be able to activate it from there.Activation Procedures
After you have logged in, click “Account” in the upper left-hand corner of the site. Under “Your Game Accounts”, there will be an option to “Add Game” for the NA version of StarCraft II: Wings of Liberty.
To activate, just click “Add Game” and you will immediately have the NA license on your Battle.net Account.
The in-game region selector will be integrated into the StarCraft II client. You can choose which region to play in before logging into your Battle.net account.
IMPORTANT: Be advised that patching and maintenance takes place at different times in each region. As a result you might be temporarily unable to access SEA games if you download the latest patch by connecting to NA.
If you connect to the NA region with a new patch, you will be unable to play in SEA until this region is updated to the new patch as well, typically a day later. Once all regions have been updated to the same patch this will no longer be an issue. Please take this into account when deciding when and where you'll play during patch days.