I am currently developing a new RSVP form available for PRO/Upgraded page users. This form allows for unlimited submissions. You can view a sample of the form here: https://customcountdown.io/rsvp?id=sample.
To view submissions, open the edit page for your countdown and click the link located at the bottom. You must be logged into the same account that was used to create the countdown page. Additionally, you have the option to export the submissions as a CSV file, which can then be sent to others.