To expand on what TomD8 said, the credit is not supposed to be equal to your total NY tax, and probably will not be because NY rates are higher than NJ, as LindaB1993 pointed out. The credit is the amount of NJ tax that you would have paid on the income if it had been NJ income instead of NY income.
The following is from New Jersey Publication GIT-3W (page 2).
"This credit minimizes double taxation of income that is already taxed by other jurisdictions. Though the credit reduces your New Jersey Income Tax, you are not necessarily entitled to a dollar-for-dollar credit for the total amount of taxes paid to the other jurisdiction. The credit represents the amount of New Jersey Income Tax that you would have paid had the income been earned in New Jersey, or the amount of tax actually paid to the other jurisdiction, whichever is less."
For more details about the credit, you can download Bulletin GIT-3W from the following link.
GIT-3W, Credit for Income Taxes Paid to Other Jurisdictions (Wage Income)
