I'm trying to set up autotiling for this tileset in Godot:
I set the peering bits like this:
However, when I try to place the terrain tiles, all I get is this mess:
What am I doing wrong?
You set some of the bits incorrectly for certain tiles, leading to misplacements in your tilemap.
Peering bits tell the engine how to fill a tilemap cell depending on neighbouring cells; it seems you used them to mark the walkable surface of each tile instead, which is not the intended use.
Here's a comparison between your setup and a tileset I adapted to resemble your arrangement (assets by Buch), with red dots marking the missing peering bits:
After updating these peering bits, painting terrains on your tilemap should produce consistent results (here I used both the Connect and Path modes):