Amazon 8706C? <-- Maybe? Everything I see shows it to be a manual charger, meaning it does not shut off.
If that's the case, I would stop using that charger honestly, it's going to end up killing batteries. Set it and forget it automatic chargers don't cost that much anymore. Even ones that automatically detect battery types (conventional, AGM, GEL) don't cost that much compared to a battery.
I wouldn't worry about it, whatever is done is done. It works right? You may have shortened the life span some, but that's probably the worst case.