This is what I send, but I do like the wording by DeliciousDesserts... would you mind if I adapted mine to include some of your wording, please?
This is just a courtesy email to enquire whether you would like to go ahead and book the date you enquired about?
As you can appreciate I do get lots of enquiries and therefore have a 10 day holding period from the date I send out quotes.
Please feel free to come back to me if you have any queries regarding your cake, but please be advised that after 10 days the date is released to further potential enquiries and so I cannot always guarantee the date will be available for you after this time.
If I do not hear from you I will assume you no longer wish book the date and I wish you all the very best for your forthcoming wedding.