I spent sin points to buy a new rifle from the witch. I died and had to start again. In the room after the bar, I can see the gun I purchased sitting on the pillar to the left of the main door. I can’t seem to access it. I have tried rolling but I end up falling into the pit below.
You aren’t able to. This room is just a bit of a showcase to let you see how far you have come I think. You will start off with whatever guns appear in front of the door. The difference now is the weapon you purchased has a chance of randomly appearing in the dungeons as a free pickup. Rather than finding a weak shotgun, you might actually find the weapon you spent the sin points on.