Take a small smooth polished piece of steel, about 1/4" thick, round the edges slightly. Then hold the gun flat in your left hand, lay this polished piece on top of the side plate junction where you caused the deformation and give the piece a tap with a small hammer. This will drive the displaced metal pack into place.
As easy as it was to move out it will move back. Having the corners and edges rounded of the intermediate piece will prevent any marring.
Ya, you made a mistake. Its a small one, learn from it. As much as we would like them to remain pristine, unless you only handle them wearing clean cotton gloves and never fire them, holster them, they will slowly get some character".