how to apologize to my boyfriends mom...

let me start by giving you a backstory i have been dating my boyfriend for two years. his mom, who likes to have the control over everything and is very set into her ways already doesn’t like me. she claims that because i’m quiet and “don’t talk to her” i am rude and disrespectful. keep in mind that i am a pretty shy person, and i reply to what she asks and will follow up with a question for her but i am not sitting there talking to her the whole time either. anyway, his mom found out that my boyfriend and i had said some things about her. for instance he had said how much he hated her and wished she was nicer to the both of us. obviously he doesn’t mean that he hates her, it was just the heat of the moment. as for me i said she was snotty and got everything she wanted so i couldn’t possibly understand how she could be unhappy all the time. she took offense, and now i am pretty sure she really hates me now. i know i need to apologize and make things right but i really can’t find the words to say it. any advice on what to say and how to go about it?

NO NEGATIVITY PLEASE!