You have to create a custom sharing rule for the page that you want to make public. Go to settings>sharing>scroll down to custom sharing for the “Pages” object. Create a sharing rule that shares the page named (Enter your page name here) with the guest user. Sharing with guest user is a new sharing option recently added and is now required by salesforce to make anything available on a public site.
If your page displays or collects records to or from the guest user from an object, you will also have to share those records in the same way.
hope that helps!
