if I understand you correctly, you're having trouble getting the bolt into the gun and once in, trouble getting it into the proper position.
Having owned three Mossbergs, I can feel your pain. It was a long time ago, but I can still remember how it more than an hour to get the thing put back together the first time.
As someone else already stated, you shouldn't have to fight the bolt to get into the gun. Before trying to insert the bolt into the gun, depress the 'button' on top of the bolt. It should be fully depressed. This makes insertion a bit easier, though it still requires a bit of digital dexterity to get it to slide over those two 'bumps.' Once the bolt is past the second bump, it should kind of slip into a slot, with no real play in any direction.
Once you get to this point, slide the bolt forward so that you can see the entire ejector pin in the ejection port. Reassembly should be as depicted in the video from this point.
Note: At first, I tried to baby my Mossbergs while trying to disassemble/reassemble them. Then I watched a competitive shotgunner buddy of mine do it, and I realized that I could be a lot firmer with the thing without fear.
Second note: When re-installing the bolt slide, after making sure everything is properly aligned, you should press the slide firmly down into position until you hear a small click. Use your thumb to slide the slide/bolt assembly back and forth to make sure everything is good to go. It should feel as if it is a one piece unit if you've properly seated the slide onto the bolt.
Hope that helps.
