I have no idea on the "expansion panels". I've never dared to get that close to one of my itchy new worlder's to check.

I think you have a female. If you can angle the shot that you took that it's more of 45 degrees to the left or the right, it might be easier to see.

Basically, you're looking for a flap in the middle. If you have a fairly large flap (and brachy's are easy to sex this way, especially at the size of the spider you have) you have a female.