Are you in a panic to get this done? ie: Without a job right now, or really need to get this done ASAP? If not, I believe you could do it by mail.
But if you need to go, then follow ertes instructions about driving and parking at the Duty Free shop.
Is your TN straight forward, or is it complex (Engineering Technician can be a little tricky from time to time, and Management Consultant is horrible these days.).
If it's straight forward then you should be okay. I believe that een if you get turned down, you still come back in a tourist capcity. You could call ahead and ask.
If you haven't been there before, it's a zoo! That's not meant to scare you but just to prepare you. It is a little frustrating becaue you will know more than they will when you get there.
Are you in SoCal?