Some students who aren't sure what they want to study in college worry that colleges might hold that uncertainty against them. They wonder if applying as an "undecided/undeclared" major makes them less appealing than an applicant who's declaring what she wants to study.
Thankfully, as long as you're applying to the right colleges, you won't have to worry.
Colleges that offer the undecided/undeclared option are perfectly OK with students choosing it. It's a college's way of telling you that they don't expect every seventeen year