I just got my first Stegadon.
Overall, I am not overly thrilled with it as a plastic kits... The gaps aren't too bad, but there are a lot of them. They could have cut out quite a few pieces IMO. Impressively though, there are pretty much no mould lines on any of it.
I had the same problem as the OP, around the neck it doesn't go together very well. I would almost sugest trying to put the neck on before the two top pieces, and see if it goes better that way. Will do a dry run with my next one.
Two little warnings, when you get to the back of the steg above the tail (part 2c in the instructions) definitely put the two smaller pieces in before the large one, do a dry run. I put the large one on first and the small ones wouldn't go in without clipping the pegs and using force.
Also if you decide to use the head with the open mouth, put the tougue in place before putting the two sides of the head together. Otherwise it pretty much won't go. Luckily I noticed that before gluing.
On to the howdah now I guess.