Teen Pregnancy

I’m 4 weeks late on my period and I’m afraid I’m pregnant. About a week ago it came back negative but research said retest because they are not always accurate. I’m 17 years old and my boyfriend and I of 3 years recently became sexually active. I don’t know how to tell my mother about it if I am pregnant and I know she’ll be so disappointed since she got pregnant with me at 14🤦🏼‍♀️. How is the best way to tell her ? I really need help