OK. Its not a big deal ***DON'T*** re-drill and tap if you can. If it leans before 12 O'clock you can tweak the barrel tighter 1 or two degree if you have a proper barrel vise and wrench. It wont affect headspace noticeably. If its after 12 try putting paper shim's under it and see if it looks OK. If it does, use a ball mill or invert the site and use a fly cutter to take light cuts off the opposing side, or use a half round file to tip the site back straight. DON'T DRILL A BUNCH OF HOLES IN IT. In the future buy a sit jig or make one. The Forester is the best and its actually to short but its all that's available. Then work as follows.
(1) Clamp the barrel of the gun, complete in a padded vise on the mill and level by eye using the complete gun as reference.
(2) Install a weaver or other flat scope base to level off of and use a machine level to note the level.
(2) Set the barrel up on V blocks in the mill and use the pre-established level to go by. Always second or third guess what you are doing and eye ball it again. If it does not look right go through the procedure again. Always trust your eye when installing sights not the measurements. If the measurements are right its perfect but always double check with your eyes. Nothing on guns is straight or parallel.
(3) Best bet is to buy a forester jig and do what I have outlined for the mill. Even the Forester does not guaranty results.
What ever you do don't panic and drill a bunch of holes. Kids do that. Its going to cost you some time. Just fix it, buy the proper tooling and think about what your doing and don't do it again. Always remember NOTHING on a gun is straight, square or parallel! Because in most cases, idiots, lawyers, engineers and machinists make guns. Not gunsmiths. Always trust your eyes over the complete gun and not just a few parts. Installing barrels or making receivers or barrels from scratch is child's play because its all simple math and machining. Making stocks or installing sights is artsy/fartsy crap and requires a certain madness. For the most part it does not come with numbers to go by.