In the final version of the counterfeit meeting, Weyoun takes potshots at Dukat and brings up the death of Ziyal, while Damar defends his former mentor. This bickering is revealed to be Garak's contribution to the recording. While the bickering is meant to add authenticity to the forgery and make them seem more lifelike instead of scripted 'actors', don't forget that Garak hates Dukat for a wide range of reasons and equally hates Damar for killing Ziyal. So it's also Garak's way of sticking it to both of them (and being the only one in on the joke).
If you believe the theory stated elsewhere on this wiki that Garak was secretly the one who supplied the data rod in exchange for the gel and then used the gel to destroy Vreenak's shuttle, consider this: 85 liters of gel wouldn't be inconspicuous on a shuttle, and it wouldn't take that much to destroy the shuttle while ensuring that the rod survives intact. This means that Garak could still have a sizeable quantity of dangerous bio-memetic gel. What might he use it for?
We don't know if it stayed 85 litres, or if the process of turning it into an explosive involved distilling or reducing it somehow to a hazardous enough concentration for that purpose. There are certainly mechanical and equipment spaces on such a craft (or even a fuel tank) where Garak could well have placed a bomb in such a way that a miffed senator and a couple of guards likely wouldn't think to inspect, especially as they were focused on getting back to Romulus with the incriminating data rod to expose that Starfleet had tried to pull a "vile deception" on the Empire. As for what quantity it takes to blow up a shuttle, these are fictional materials and we just don't know what the explosive power of a biomimetic-gel-based bomb would be. It's also possible that Garak used some to create the device with which he all-but-confirms he booby-trapped Tolar's door to keep him locked up.
The more likely explanation is that he really did have to trade the gel for the rod, rather than already having the rod himself (tricking Sisko out of a large amount of a highly-controlled substance solely to get his hands on bomb material rather than just giving him the rod would smack of Complexity Addiction), but he kept some himself just in case (perhaps his contact only asked for 80 litres and Garak tacked on the extra 5 for his own use).
