Can you cancel an agreement being a guarantor?

No, you can not stop being a guarantor to an agreement while the terms of that agreement are in force. Thus if you are a guarantor for rent and the person your are guaranteeing fails to pay the rent - YOU must pay the rent.

If you a guarantor to a loan and the person with the loan defaults, YOU must pay off the loan.

This is what it means to be a guarantor - you can not get out of the agreement when things begin to go wrong.

Think VERY carefully before being a guarantor to ANYTHING.