Sure. It is possible that the contract could be upheld as written if the employer challenged it.
However, warn59 has said he believes the rate of pay entered could have been written in error because it did not reflect the oral agreement.
From the Restatement (Second) of Contracts, Chapter 6, Mistakes.
Section 152 (1): “Where a mistake by both parties at the time a contract was made as to a basic assumption on which the contract was made has a material effect on the agreed exchange of performances, the contract is voidable by the adversely affected party unless he bears the risk of the mistake under the rule stated in section 154.
Section 152(2): In determining whether the mistake has a material effect on the agreed exchange of performances, account is taken of any relief by way of reformation, restitution, or otherwise.”
Section 155: “Where a writing that evidences or embodies an agreement in whole or in part fails to express the agreement because of a mistake of both parties as to the contents or effect of the writing, the court may at the request of a party reform the writing to express the agreement, except to the extent that rights of third parties such as good faith purchasers of value will be unfairly affected.”
I think the consensus of members is that warn59 should speak with his employer. I agree.