At the airport this morning I used a VDB voucher to ticket an itinerary (BWI-ORD) I placed on hold online. Later today, I checked the price of the same exact itinerary and the price dropped $100, so I now want to purchase the itinerary with $$ and save my VDB voucher for later use.

Is this possible? How can I get my VDB voucher back and pay for the ticket with $$ instead?