Accidently urinating on the musalla in a mosque

about 6 years back, I accidently(due to lack of control) peed on the praying mat in a mosque which was placed in open sunshine on the floor of mosque. at that time nobody was there watching me and I ran away. now whenever I remember that I curse myself for being responsible for that najasat and ruining the muslims prayer who pray on that mat.
please guide me what can I do? I am so desperate. I don’t know about that mat now, because I did not go to that mosque since years.