It’s better to do a full blueprint and do everything I’ve seen threads out anywhere from .005 to .020 or .025+. IMO if your already set up to cut the face might as well do it all and then the bolt too and have everything done right from the start
Take it to a gunsmith and let him set it back one turn, if you try it yourself it doesn’t take much to ruin a chamber and could end up costing way more then just having it done right the first time