How do I cancel a parenting plan?

The court can modify a parenting plan so long as there is a "substantial change of circumstances" OR you both mutually agree to change it. If both of you are in agreement to change the terms of the agreement, then you can modify it and also modify child support based on any new timesharing. I would recommend you consult with a licensed attorney to discuss your options.
Best of luck!

You have a lot of things going on here in one question. If the Judge has approved the parenting plan and made it part of a court order then the way to modify it is by filing a supplemental petition to modify. You would also need to convince the judge that there has been a substantial change in circumstances. If the Judge has not "signed off" on the parenting plan yet then you need to move quickly in trying to get the parenting plan agreement set aside. This means that you would be trying to get out of a contract which is not easy. You will need a valid legal basis and need to move quickly if this is the situation. Sit down with an attorney in your county immediately. You also mentioned moving 65 miles. Keep in mind that relocations greater than 50 miles after entry of any custody order triggers Florida's Relocation Statute 61.13001. This statute is very strict and unforgiving so anyone divorced with a kid should read it.