I had the same issue with a Galco shoulder holster that sat for over a year without a gun being put in it. It took me a long time to finally get it snapped!
I think you'll find it'll be fine in a couple days. You might order some Galco Leather Conditioner, its what Galco recommends. If it's still too tight, put the conditioner on the rough side of the leather that goes around the hammer, cover that part of your gun to protect it from moisture, re-snap the holster and leave it a couple more days.
