Sage correction

Hi, I was hoping that someone would be able to help me.
In sage I accidentally recorded an invoice as being paid from the petty cash account. I have raised a dummy credit note to put this right but when I try to post it sage says that "there is an unallocated cheque balance" My petty cash on sage is now negative because I made the payment from it instead of the bank account. How can I stop it saying this and put it right. When I paid the company I did it from the correct bank account.

Thank you for the help :-)