The IRS will consider those payments as payments towards your 2017 Federal tax, and will most likely refund the excess (if any) to you. (Be certain to claim the state estimated payments you made to the IRS by accident, if you have not already filed.) If for some reason they are not refunded, please contact the IRS and request a refund of the overpaid amount.
I recommend that you call your state and explain what happened - some states will give you a one-time penalty forgiveness in a case such as this. You will probably still have to pay the interest, however, if any.
