I damaged a car that is going to cause owner to miss an event he had paid for in advance, am I responsible for property damage and event missed?

I borrowed my co workers truck to do a side job. I was not in an auto collision, but amidst doing the job, I slammed the tailgate of the truck closed and it cannot open anymore. In a couple of days, he was going to use the truck to haul his motorcycle to a race track for an open track day where anyone who pays to go and race at the track can go. Needless enough to say, he had paid for this "track day" in advance and since the tailgate cannot come down it will be merely impossible to load the motorcycle in the truck and take it down to the track. The damages to the tailgate are probably not going to be fixed in time for the track day and was wondering if I am now responsible for paying for his track day