Looks like you did a good job on a first holster. I make a lot of holsters and line very few of them when requested by customers. To keep the snaps from scratching the gun I try to position them in a place where the gun will not rub on them when inserted in the holster. Between the cylinder and the trigger guard seems to be a good place to place the snap.
Also I do try to cover the trigger but just because I like the looks of it better that way.