You should cancel the plan immediately. Next, you can contact billing support and ask, but refunds are not offered unless there is a fault in the service.
Billing issues, as the banner on the top of this site says cannot be handled by this community.
To add to what @free999 said, here’s the relevant portion of Cloudflare’s terms of service that addresses refunds… which you agreed to when you signed up:
4.3 No Refunds
FEES ARE NONREFUNDABLE. YOU WILL BE BILLED IN FULL FOR THE SUBSCRIPTION TERM IN WHICH YOU CANCEL AND NO REFUNDS WILL BE PROVIDED FOR THE UNUSED PORTION OF SUCH SUBSCRIPTION TERM. Following any cancellation, however, you will continue to have access to the Paid Services through the end of your current Subscription Term (except with respect to Services subject to usage-based billing). We may, in our sole discretion, provide a refund, discount, or credit (“Credits”) to you in a specific instance, however the provision of Credits in a specific instance does not entitle you to Credits in the future for similar instances or obligate us to provide additional Credits.