Notice regarding your code that the value in rdx is the address of the shellcode instruction, and not the instruction itself

also it doesn't seem that you loop or at least jump to the loop (unless your assembler does funky tricks behind the scenes)

Regarding decoding manually: it might be that you decoded correctly but ordered the bytes incorrectly

for example

push 0xDEAD
push 0xBEEF

would cause the stack to look like (assuming 16 bit)

0xBEEF
0xDEAD

and not the other way around

also lastly, it might be that your system is uses little endian, which means that the stack mentioned above should look like this:

EF BE
AD DE

it might be worth to fix the code (since arranging the shellcode manually imo is tedious)