Certain days on my calendar are blocked. How do I fix this?

I did check your form and found that you have added "Date Reservation" widget in wich you have disabled past dates.

Please note that how this widget works is when a user select a date and submit form, the same date will not be available for other users. That means same date cannot be selected by two different users. 

Hope this helps.

Do get back to us if you have any questions.