Proposition: If $x$ is even and $x$ is greater than $2$, then there exist prime numbers $p$ and $q$ such that $x = p + q$.
Contrapositive: If for all prime numbers $p$ or $q$, $x$ does not equal $p + q$, then $x$ is odd or $x$ is less than or equal to $2$.
Yes, your contrapositive is pretty much correct. All I would do is change the word "or" to "and":