Hi @Lu-and-James0
Your booking is covered by Airbnb's long term cancellation policy https://www.airbnb.co.uk/home/cancellation_policies#long-term
I would recommend you have a read through airbnb's help centre and the useful guides on the community centre as it will help you get to grips with how airbnb works which in turn will help you manage your listing more succesfully and avoid some of the common pitfalls.
You cannot take a deposit with Airbnb. Why not change your cancellation policy to strict.
Don't forget guests (as well as hosts) can cancel under Airbnb's extenuating circumstance policy regardless of your cancellation policy.