If it's room only, penalties hit when you are within 5 days. If it's a package, you fall under Disney's cancelation policies, which is $100 fee when you are within 44 - 6 days prior your trip.
You might want to find out if you change your dates to September/October now, and sometimes Disney will waive that fee since
AAA is a big seller of them.
Sorry you have to change your dates

(I'm not going to say cancel! You're just traveling at a different time!)

ixiedust: