A real apology has no “but” in it. The moment you add one, it turns into a defense.

The word but deletes everything in front of it. An apology with a clause attached is a defence wearing an apology’s clothes, and the person hearing it knows instantly, because the second half is busy explaining why you were right all along. Sorry and an explanation can both exist, just not in the same sentence.

Next time, say what you did, say you were wrong, and stop talking. Skip the context and skip what they did first. If something genuinely needs explaining, offer it a day later.