Setting timing ? First time doing it.

Hello, I was able to get an old Sears timing gun off Craigslist from someone not too far.
On another post in this section I was advised to check my timing. The fender sticker on my car 1976 Dart says 2 degrees BTC.
I’m watched videos and read on how to do it. What confuses me is do I line up the notch on the crank pulley with the tab that says Before and 2?

When I checked it now, the notch is lined up to zero(Between After and Before).
I tried to twist the distributor to retard it to 2 Before, however the distributor won’t twist anymore. It will only twist in one direction, thus advancing.