Am I doing the right thing as a mom?

A while back my daughter and I had a conversation about sex and what not (I didn't have such an open relationship with my mother so I want to be there for my teenage daughter). Well when we had this conversation I told her that if she chooses to have sex before marriage (which I hope she does) to come to me and I'll help her prepare so she's safe- meaning bc and condoms or whatever she needed. She agreed but we both had in mind that she would be older like 18 or 19

Recently she came to me and said she wanted to have sex with her boyfriend of a little over 1 year. She's 15. She keeps trying with me but I never told her I would help her at 15. She gets upset with me because of our agreement but I think she's too young. Am I doing the right thing?