@Jimmy182 discounts don't magic themselves onto listings.
You chose a 20% special offer discount when you published your listing
You chose a 40% monthly discount under pricing
You chose a 21% weekly discount under pricing
The special offer discount is added to the weekly or monthly discount giving your guests upto 60% off.
You can't fix it without creating other problems.
you can ask the guest to pay more (they don't have to) = negative review from guest
you can cancel the booking = cancellation notice on your listing and other penalties.
Or you can honor the booking, you have with this guest