Don’t get discouraged. The hammer needs to be forward (uncocked) when you put the halves together so there’s no extra tension on the springs. The trigger and trigger bar should move forward under spring tension - you shouldn’t have to push them forward manually. If they don’t, something isn’t installed right.
Once you get the hammer cocked and are putting in the safety, you have to put a tool in the other side and move the trigger bar out of the way so it can slide in.
I recommend watching the Ultimate video again - it’s probably one of the clearest how-to videos I’ve seen. Relax and take a breath - I’m sure you’ll get it. Lots of us here have done the upgrades and we’ll help any way we can.