You may want to pay on the 25th March instead of the 31st March. Your gross sales up to the 25th is $100 but you are expecting more sales by the 31st March. You can estimate how much sales you might get.
If you believe you will receive a further $20 for the remaining period. Instead of declaring $100, you can declare $120 which includes the $100 of actual sales and the $20 estimated sales.