Question.

[xOchiix]

Ignore [But please don't. xD.] this nOOb question.
But I can't pick up my pre-regged badge today,
so is the pre-reg line different to the line where you buy
that day?
Where is the line?

[SOawesomeness]

Pre-reg is where you pick up early and pre-reg. It should be right in front of you when you enter the SJCC from the main entrance.

At-con is where you purchase one day or whole weekend memberships. When you enter into the SJCC from the main entrance, you'll walk to the right on the first level and see a line-place/line... that's where you go to start the process of at-con.

[xOchiix]

So today is the day when I can only purchase at-con badges?
I'm so confused.

[GokuMew2]

So today is the day when I can only purchase at-con badges?
I'm so confused.

Correct.
After early reg closed, your only choice then and now is to register at-con.

[Kandybar]

If you pre-regged/early-regged, there will be a separate line at-con to pick up your badge.  There are two lines.  If you didn't pre/early register you will need to stand in the line to purchase badges.  If you're confused, there should be a staff member in the general line vicinity who can help you out.