I had the same problem last year when I built my GP rifle. If the hammer doesn't line up square it won't fire every time, which is good if your working on target panick (flinching), but not when your hunting. I didn't know what to do about it because this was my first attempt at gunsmithing, so I went to a gunsmith and he told me to grind a little off the lock plate. BAD IDEA!! I went home and did just that and the alignment didn't improve, but I did have a gap between the lock plate and the barrel, which now I have to look at every time I shoot it. So what I did was simply unscrewed the hammer screw, took off the hammer put it in a vice. Took the handle end of a cresent wrench and bent it ever so slighty. Being its hard cased the gunsmith didn't think you'd be able to heat it. If you don't have to go a lot I think cold bending it should work, just be careful and don't over do it. If the lock plate isn't sitting flush with the stock you may only have to remove a little wood.
chris