DHSF - I say your response is quite normal, you should (if it is a repeated trait your mother is showing) confront her, but not whilst your emotions are high, just keep a mental note, that when you are in a good moment you will bring it up and calmly and kindly tell her that it is your fault, but when she does X that it upsets you and makes you less likely to be able to be a good person (ensure here that you emphasize that it is your fault, all women seem to want to hear that) as it throws you off course. Without knowing exactly what it is difficult, but if it is trivial, whilst in this mode of subserviant son, it may help to explain that the situation makes you less able mentally to deal with whatever is underneath and causing it.
Though if you are really in the wrong and she has called you up on it be a man and say sorry! (I hate doing this but have to, as, just occasionally I am wrong!)