Wite it all in an email or on paper, and give them your explanation/apology that way. At least then they will have the bulk of the information about whatever mistake you have made. At the top, tell them you are writing it down so you can get it all out straight, and at the end, tell them you really want to talk about it, but if you had tried to tell them this verbally, you would have just been crying. Then, send it and give them time to think about what you've told them- and how they feel about you. That might take a few mintes, oir a few days. Give them time.