I've been having exactly the same problem as described on http://cs.elderscrolls.com/constwiki/index.php/User_talk:Kovalai. When the game loads up I'm set to the default starting character (despite having changed this completely in the construction set) and I'm located under an Ayleid Well in coordinates 0,0 in the Tamriel world space instead of an interior I made from scratch.

I've looked everywhere for a solution but I can't find any help.

Changing the ini to test your mod is one of the most silly things I've ever read in a tutorial. Someone should correct that. I don't know what went wrong or why it went wrong in your case, but the easiest and by far superior way to test your dungeon is to simply use 'coc [cell name]' in the console to teleport to your cell. Like

coc AbandonedMine

will teleport you to the Abandoned Mine interior cell.

No need to mess around with the ini.