At 15:54 you extrude some faces to get faces to loop. I've repeated the actions but instead of a loop get some gross distortions and no looping obviously. What am I doing wrong?
https://imgur.com/8Zh6cat
Also why is my sight looking funny like that?
https://imgur.com/uigUFRI
Hey, the reason it doesn't loop is because the normals flip at that edge. It's hard to explain in text, so here's an image. The red represents vertices that should be deleted, and the green lines show what should be filled in as faces to match what's in the video. After doing that, recalculate the normals and you should be good to go.
For the sight, it looks like you have an interior face right in the middle that needs to be deleted.