Girlfriend's mum caught us having phone sex, what can I do?

Well, yesterday my girlfriend’s mum caught us having phone sex and she had a go with her, and believed that we were making out in her room when I stayed around hers some weeks ago.

She was angry and told her she shouldn’t be doing that with me and she should be working out on her studies instead of ‘playing around’, because she thinks my girlfriend is too young to do such a thing with me (she is 17), and she thinks we might not even last (which I agree although I still love her loads) . She was going to call me but my girlfriend stopped her, and said to her mum that she wasn’t harming herself or having sex with me.

My girlfriend’s parents are very traditional and quite protective so although her mum liked me a lot, I don’t know and I am not sure what she thinks and how she sees me/us now. I don’t know if she likes me anymore.

I tried to tell my girlfriend to talk to her mum to ask her what she wants and talk to her about it, to show some respect toward her by listening to her, but my girlfriend said just to leave it.

However, I have an urge to talk to her mum, because I want her to know that what we really think and I want to get it cleared off our heads. Also, I want to avoid any hassles in the future, that’s what makes me think that I should talk to her about it.

Should I talk to her? or should I just listen what my girlfriend said, just to leave it unless she said something? If I should talk to her, how should I start? We have some distance away, so I can only talk to her on the phone, how should I start the conversation?

so should I just leave it, and just wait and see how it goes?

what if her mum calls or try and talk to me in any way

What do you think I should do?

Since it has happened, I am trying to find a way or anything I can do that is more ‘ideal’ to the situation, so it is best for everyone.

I know I sound silly and I know I am immature, and I need to grow up. But I want to have a good relationship with my girlfriend and her family, so I am trying my best to please everyone, and I know it is hard. And everyone learns from mistakes, including me.

Please help! Many thanks.