This is how part 1 and the join piece (the bit with the teeth) should look. It should be inside part 1, as shown:
Here is part 1 and 2 joined together the way they were meant to:
Inside view:
Part 3 to be joined:
This is part 3 under a very little weight while the glue dries. I use old blade boxes that have the used blades as my weight. This keeps everything flush while the glue is drying:
Finished this bit. The overhang is not as bad as it looks. It is more a light shadow but a little sanding will fix this:
How it all goes together inside:
To be continued....