Eight hundred grams on a long snake isn't the same as 800 grams on a short snake. His body has a triangular shape to it in your pictures, not a rounded look, which indicates that he is under-weight.
For comparison - you can see the spine on yours, vs a male at about the same age the picture was taken at about 1000 grams:
and then yours:
Can you see how much more filled out the first picture is? This male is now 1500 grams.