By deeper I mean 1/16" at a time, check your to see if your trigger is picking up the sear. Chisel and Exacto only, no hook knife. The hook knife has no safe use in gun building, carving tools, rat tail files, and riflers get the job done along with lots of sandpaper. I frequently do my final shaping with sandpaper to keep from being too aggressive.
When inletting deeper you never work on the sides of an inlet, only the bottom. You can make a workable skew chisel out of an old screwdriver or fleamarket chisel to make working the bottom of an inlet easier. I use an 1/8" wide one more than anything.
The first thing you want to do is pull your lock and see how far your trigger goes up in the lock inlet, then try to see where your sear is positioned in the inlet. If they are way off you can add more metal to the top of the trigger bar and leave your inlet alone.
Added metal; I have done it several times when my trigger didn't quite hit the sear enough to trip it.