Fess up to the owner(s), get the mechanics estimates done, file the insurance claim or whatever it takes to get the planes fixed, and make an incident report to ASRS. Try to avoid placing the blame anywhere in the report, just tell what happened. You probably will never hear about it from the FAA. In the future if you are asked on a job app about it be honest and say it was a moment of inattention but leave out the part about how they other guy was stupid and the plane was not where it was supposed to be parked. You learned not to do that anymore and it was a hard lesson and you have been 100% safe ever since, even when others are not adequately safe. It will probably have no effect on your flying future, or if it does then you probably do not want to work at that company anyway. There is a damage definition in the NTSB rules, check that out. I think it's anything over $25k must be reported, so maybe you can get out of making an NTSB report if it's less than that. This too shall pass as they say. We all have a bad day every now and then- it's how we deal with it that counts.