if you really wanted to, you could try calling them about it and see if they will let you send them the money, although i would think they would just say not to worry about it, but it’s always good to find out first and not just assume they wouldn’t care.
but don’t let this stress you out, you didn’t do anything malicious and you certainly didn’t do it on purpose, it was just an accident, and it’s not a mortal sin at all, i’m not sure if you could even consider it a sin at this point, because you never meant to leave it without paying, and now that you’ve realized it you want to pay for it, so i don’t really see any sin here…i think it would only fall under sin, and only venial sin, if you decided not to because you don’t care,
just do what you can when you can, but don’t let it rob you of your peace, it’s not a big deal, although i think it’s good to be concerned, but don’t go overboard with it, it’s enough that you try to do you’re best to do what’s right, and then that’s all you can do.
i’m not trying to belittle the situation though, so don’t get me wrong, you should try and pay for it if they want you to, but all i’m saying is, don’t let it stress you out, it’s not good to be stressed out even with our sins.
ok, hope this helps, take care.