if you used it while it was at your house for running to the store or anything else not work related, then it was for personal use.
I have a hard time believing this is about you using a car to run to the store though. Even a court would not likely see an issue with such use determining it to be de minimus and as such, so trivial as to not have damaged the company enough to concern the court with the issue.
is there something more to the situation?

