Keep the bike stock. Your butt is supposed to be a bit sore when you start cycling and there isn't a saddle in the world that will change that. The fore/aft position and tilt of the saddle, as well as height, are far more important at this point. You can't possibly know what your preferences are going to be until you've been riding for a while. If something feels wrong right from the get go, even on short rides, it's more than likely a matter of fit rather than an issue with the quality of the saddle. Keep the saddle for now.