Just a small piece of advice from an amateur flint builder, your chisel's do not appear to be sharp enough.
Before I sat down to work on fitting I would take my chisel's and dress 'em up with a good quality stone. Then I made a leather "strop" for my drill press. I took a piece of leather, cut about 8 same diameter round pieces about 2" in diameter, and "stacked" them on a bolt. I then (using washers on each end) wrenched the stacked leather down tight.
Then using a polishing compound (choose any find compound....Flitz, Valve grinding, etc) I would polish the chisel's to pretty much razor sharp.
You will find your cuts much cleaner and easier to do.
I hope this helps.