"Comparison failure at Line 3" have not idea why the Not gate can't out 1 when a equal to 0.
Your HDL is correct. Please edit your post to remove the HDL code.
The most common cause for failure on line 3 is that you are testing Xor.hdl in projects/01 without first completing and testing Not.hdl.
Because the Not.hdl has no implementation yet, its output is always 0.
You must build the parts in the order presented in chapter 1. Not, And, Or, Xor, ...
The chips you build become building blocks for the later chips.