mmm Glenys, why not just a simple "Sorry" or "I'm sorry"or "Well, I made a mess of that, sorry."
"My bad" would reflect a cultural inclination to the simplistic and semi-literate standard as being acceptable use of language, much in the same vein as "never ever", perhaps. While I am certainly no Grammar Nazi, see this very funny YouTube video clip, YouTube video
I do like my English to be almost accurate.
I would much prefer the English of Dickens, or Joyce, or Shaw or even the Dreadful Dan Brown to "my bad". Equally, I understand that the dynamics of language often drive it in directions the purists would not want to go and after a short time colloquialisms can often become part of the language but not all of them are really beneficial, or edifying. I also accept that many, many more colloquialisms are used in a specific era, for a specific purpose, then dropped by the next generation as being inane, or no longer serving the purpose they did serve. Please look at the wonderful documentary video by Melvin Bragg on "The Adventure of English" and you will get a better sense of what I am talking about here.
In this short, for me, gripe there are several grammatical errors, a run on sentence and a dangling participle. I am sorry I did not pick up on this discussion earlier, I wasn't really paying attention, you see.