It is not your mistake. The breech is in the recess provided in the lock plate. You are painted into a corner.
You can not move the tang back. One the recess in the lock plate will be wrong if you do. Also the tang is wasp waisted. If you move it back you will make gaps around the tang.
Hawken's are hard. Seeing this stuff ahead of time is not easy. Did the hammer fit with the lock plate out of the stock with the plate situated in the bolster recess? No? There is a big problem right there. Then you had a precarve stock. The options are limited.
Ask whoever sold you the parts set for their advice. I think the only option is to modify the hammer. I like a little tip and an oxy acetylene torch. With that you can localize the heat and bend exact places on the hammer.
The thing to do is to get your stock with no lock inletting. Inlet the barrel and tang. Then figure where the hammer needs to pivot. Inlet the lock plate according to that. Then cut the recess in the plate for the plug bolster. This is why precarves are sometimes just firewood. It could have been worse, your parts appear to be usable.
On my Hawken build I got two junk precarves in a row. I sent the first one back. The second one appeared to be OK at first. IT was not. IN the process I ruined my lock plate and hammer. I regrouped and made my stock from a plank. That worked just fine. I will never build from an ordinary precarve again.