I was 19 when I told my parents I was pregnant. It was the scariest day of my life. I called my mom (cuz she lived 2 hrs away) and said, "guess what..." and I was silent... And still debating to tell her or not... But then I blurted out, "i'm pregnant." at that moment, I swear, I felt like a million tons of weight just lifted off my shoulders. O, trust me, it was damn scary, but also felt so good. Her and my dad didn't take it too well, they were pushing for an abortion. They kind of swung between being supportive and not. That whole week, all I did was cry, because my parents were arguing with my boyfriend constantly about different matters like marriage and moving back in with them etc. But finally, they are starting to become more and more supportive and even starting to get a little bit excited about the baby. They will never end up being like my bf's parents who's been crazy supportive and loving from day one. But there is no way I can not tell them, and i'm glad I did. O.. The only regret, I told simon's parents months before I told my mom. When she found that out. She was unimpressed.
What I am guessing is... You are more afraid of what disappointing your parents, and letting them down. Or maybe that telling your parents in a way, is hitting reality. And they will hit you with a bunch of truths (like finances and the future) that you are afriad to hear.
Let me know how it goes... Best of luck.
Remember, they are your parents and they will love you no matter what.