So you signed the contract knowing it applied to part-time work, giving us no reason to believe that it wouldn't continue to apply to your part-time work.
There remain questions of whether the contract is reasonable under the law, which would depend upon its terms. If you are intent on violating the contract I suggest that you take it to a plaintiff-side labor lawyer for review, as it is impossible to advise you about a contract term without reading the actual contract.

