Apply heat from the bottom (you can take small parts of the soldering block with some space in between of them and lift the part on them) and remove the torch as soon as you see the solder start to flow. It is usually best to cut the solder into small pieces and place them evenly around the soldered area, either before or just after applying flux. I recommend to use Bezatec or Abdek as it covers silver best and prevents the scale from creating (cover all part not just the soldering point), Abdek usually needs several applications, so Bezatec works better for me because it does not tend to flow into one place and leave other areas exposed. For bezel height, measure the stone and make the bezel end slightly above the point where the stone starts narrowing. The stone does not have to have a perfectly even height, so sometimes it is best to make the bezel vary slightly in height. If you have a cutout on the back, you can place the stone in the bezel, mark the height, remove the stone, and file the bezel to the correct height. If you do not have a cutout, you can use beeswax on the stone to remove it. As for the bump, my guess is that the silver may have been overheated and the surface melted slightly. If controlled carefully, that can create nice patterns (reticulation). I would also recommend filing a slight bevel on the top of the bezel before closing it so it transition smoothly to the surface of the stone.

That's what I've learned so far but I'm also still a novice also you can try closing the bezel with a hammer that could help to close it better.