Aww hunny (hugs) , Being scared is natural for everyone no matter what age.
As the lady above said it doesn't matter what race either of you are if you are happy together & he is staying with you then that's all you need think about.
Being honest i would tell your parents soon after you find out for definate, They maybe angry at 1st & they may not, But even if they are angry that will quickly turn to a need to help you & guide you. Its a scary time when you have to tell them but you need to be strong, If it makes you feel better or more confident take your boyf with you then they can see he isn't leaving you & that he is going to be supportive. You will also feel like you have his support too.
Another way to try is to go in all guns blazing & excited & burst out with it in a fab way, Sometimes its really hard for people to be negative when they see just how happy/positive you are. When you find out if you are take time to yourself 1st though & talk with your boyf, then tell both parents. xxx