Your code is functioning correctly as written. There are several conceptual issues with your code which you should fix:
The system function $urandom() returns a 32-bit integer. You are trying to concatenate two 32-bit integers and assign it to a 10 bit variable. This makes no sense and the concatenation achieves nothing.
You are using >>{} and <<{} as streaming operators, not as logical shift operators. Please refer to section 11.4.14 for an explanation of how these function.