"I am so worried about what they would think of me."
Home/family is the one place everyone should feel safe to be themselves.
Most people want to be loved and appreciated for who (they) are.
What's the worst thing that could happen if you came out?
Can you (live) with that?
Having said that if you and your partner are fine with hiding your relationship then it's not a "bad thing".
Oftentimes it's not that the person keeping a secret has a problem as much is it is (their mate) who resents having to live in the shadows like a "booty call". Some people feel like it's a "tier two" relationship.
They feel if you truly loved them you'd shout it from the mountain top!
This is especially true if (her family) is fully aware of the relationship.
Don't be too surprised if you later learn your folks already suspect it.
A lot of families play: "Don't ask, Don't tell."