Nom -it really is ok to admit when you’re wrong.
Asking for forgiveness for a personal slight against an individual is not a “prayer”. Asking for general forgiveness would be. If i ask a deceased relative to forgive me for what i did to them, it is within their power to do so, because it’sa decision on their part, as rhey are the aggrieved party. People in all circles do this at levayos. That’s not making a request for someone to help you, feed you, heal you, give you money, help you learn torah, or anything else.
If someone asked for forgiveness for being mechalel shabbos, that would in fact be tefilah and would be totally assur.
But that’s not what happened at all.
If your goal was to prove that chazal communicated with the dead, then it’s clear that they did – but in what capacity? Did they nake requests of them as one does from Hashem? Absolutely not!