You can cancel your policy if you sell your house. You simply need to have your agent provide the company that writes your flood insurance policy with a signed cancellation form and legal documentation such as your settlement paperwork showing the title transfer of your property.
Another option would be for the buyer to assume your current flood policy through an endorsement. This would allow the buyer to show continuous flood insurance coverage and maintain the RR2.0 premium glidepath, if applicable. Check with your agent to see if this is an option that works for both you and the buyer.