It's not always easy from a shed skin to id it down to species level.
Next time, try to keep the skin as flat as possible to make all scales visible, also especially the side and top of the head. Also midbody so a dorsal row scale count is possible.
But at least it is good enough to exclude some, ;-)
For example it is 100% sure not a Monocled Cobra, nor a Spitting Cobra. And also certainly no King Cobra. Head cales in the cobras and king cobra are very different. Also the eyes are too large.
So what is it then?
Well, it is surely a harmless, non-venomous species as it is one of the rat snakes.
There are a few options there, and I do not dare to say for 100% which one it would be.
There are two genuses that could be an option.
Either the Coelognathus or Ptyas species. Both genuses have a few species. I do not know your garden, but species that I would expect in a typical Thai garden are:
1. Coelognathus radiatus, (has many common names) Radiated Rat Snake, Copperhead Racer
2. Ptyas korros, Indochinese Rat Snake
3. Ptyas mucosa, Oriental Rat Snake
4. Ptyas carinata, Keeled Rat Snake
Sadly I do not have clear head shots of all these species readily available in my messy archives, but it seems like the head scales are a bit different than what I can find in the Indochinese Rat Snake (which would be the most common of this list).
So I would guess it is either number 1, 3 or 4.
As I said all these are non-venomous. Number 3 and 4 are very large species, that could reach like 3m or more, probably these are amongst the most often misidentified 'King Cobras' that people see. Even though harmless, of course they will bite in defense, but that doesn't cause you any harm unless you are unlucky to get some sort of infection. Also need to add that these rat snakes are protected under Thai law. There is a short list of protected species and these are amongst them. At the same time these are probably some of the most hunted snakes because their size makes them worth the effort of catching and creating some Khapoa Ngu ;-)
It's funny how some of the most common snakes are protected, while many rarities are not protected at all unless inside a protected area.
Out of my head, I believe the King Cobra is the only venomous snake on the protected list. Not sure why, I guess just because it is such an iconic charismatic species.
The rat snakes and the pythons are most likely simply protected because they are very useful in pest control.