It's the best choice to be honest with your parents! I know very well of the place you're in -- I met my bf online and worried so much about breaking the news to my parents. It was scary leading up to it, so don't think about it too much. Make plans to go out to eat with them and tell them there. People are at ease when they're eating
Haha
Think of what you're specifically worried about. Figure out how to ease that worry. Usually going out to a restaurant will ease those worries because you know your parents can't get too mad in public, if you worry that they will get mad. Chances are they won't, but being out of the house will help your worries!
Parents are going to naturally worry about their children, especially if you're the youngest and they're girl. So this is a transition for both of you, and you can help them through it. Tell them about him, as much as you're comfortable saying. Ease them into it, little by little. Eventually they will be comfortable, it takes time, but know it's natural for them to be concerned.
All the best
You'll do great