Hi Smidge,
A grave headstone usually indicates that something is buried. So, this suggests that nothing is outstanding. You do not have outstanding issues with anyone, but, the fact that this headstone was about a specific person, Kathleen, which is very peculiar, it probably means that there is a small little issue still outstanding regarding her. The flowers symbolize honor and praise, so maybe you should honor her and give her praise about something she did for you in the past, which you failed to do. Anyway, in such a case the headstone means; “just sort out this small matter and then you are OK”, which means the answer to your question, “do I need to confess anything?” probably is yes, something about Kathleen. Maybe you should ask her if you failed to do anything in the past that bothered her or are still bothering her.