Rewards Campaigns on Fundable are "all or nothing." If you do not meet your fundraise goal, you cannot collect any of the funds you raised. Nonetheless, you are free to attempt your campaign again. This is why we stress setting an appropriate fundraise goal from the get-go.
Even if you didn't successfully complete your fundraise, you can still download backer data, such as personal information, contact information and email addresses. With this backer information, you can create a mailing list to coordinate with for a second attempt at the fundraise.