To the OP: as the previous poster said, there's nothing that KLM can do until check-in opens for your flights; it's not their ticket and it's not on their ticket stock; they can't assume control of the ticket until just before the flight is scheduled to depart.

You could contact your travel agent and enquire about the possibilities of now adding baggage for payment. However, they'd have to go through Virgin (you probably wouldn't be able to approach Virgin yourself to enquire, as it's not their ticket either - it's issued by the agent with whom you now have the relationship) and I'm not sure whether and if Virgin have any mechanism to add a paid baggage allowance to this kind of ticket. I suspect that this would work out no cheaper, and possible more expensive, than just paying KLM's fees on the day.

You're almost certainly going to have to wait until you arrive at INV on the day of departure to be able to arrange extra baggage for a fee. And you would probably also have to arrange extra baggage for the return trip upon arrival at ORD ahead of your return flight.

It would be really beneficial if, after you've travelled, you could come back and relate your experiences, including telling us how much you were charged for luggage.

Enjoy the trip!