If you want to reduce Clique directly to 3SAT, you can design a boolean circuit, where the input is a graph and a subset of vertices, and the output is TRUE if that subset is a clique and FALSE otherwise.
If the graph has N vertices, you need:
N variables, one for each vertex, which is TRUE if it is part of the subset and FALSE otherwise.
N * (N - 1) ...
Your evaluation only works into one direction, you can use it to test for unsatisfiability for the listed cases which are only a subset of all unsatisfiability cases.
Imagine for example a formula in which 100 clauses contain x and one clause contains (¬x ∨ ¬x ∨ ¬x).