Are you sure you selected the right choice? Because following the article below its possible pay less upfront (Im not sure about 50-50%)
But anyway if you dont want do be overdrawn right with xmas over the corner mayber cancelation is the best option and probably without any penaulty and you make new reservation soon as possible.
The Pay Less Upfront Feature allows Guests to pay a portion of a booking’s Total Fees at the time of booking and pay the remainder of the Total Fees at a later time prior to check-in. The Pay Less Upfront Feature is available to Guests for eligible bookings when they pay with certain Payment Methods. If your booking is eligible for the Pay Less Upfront Feature, the Airbnb Site, Application or Services (collectively, the “Airbnb Platform”) will notify you during checkout.
If you choose to book with the Pay Less Upfront Feature, the Airbnb Platform will notify you of the amount and schedule of each payment due. On the second payment due date, Airbnb Payments will automatically charge the original Payment Method you used to make the booking. Gift Cards and credits cannot be used for the second payment. Therefore, to the extent a gift card or credit is used for the initial booking using Pay Less Upfront, Airbnb will only charge the gift card or credit up to the first scheduled amount due.
If you make a modification to a booking made with the Feature, you will be notified of the revised payment schedule, as applicable, via the Airbnb Platform. If the modification increases your Total Fees, you may be required to make an additional partial payment of the new Total Fees at the time of the modification.
You authorize Airbnb Payments to collect all amounts due from you pursuant to these Pay Less Upfront Terms by charging the Payment Method used to make the booking or otherwise as permitted pursuant to the Payments Terms. You agree that by selecting the Pay Less Upfront Feature, you may not be able to pay for the booking with a different Payment Method or pursuant to a different payment schedule.