Welcome to our world. It's great that you're already thinking about these things, but there's probably nothing to worry about.

You've already figured out the most important thing about joining the work world: School doesn't really prepare you for it. I'm not suggesting that school is unimportant, but that it really provides only a narrow set of benefits. A good college education should teach you two basic things: how to think clearly and critically, and how to learn.

Any reasonable employer hiring someone directly out of school should be looking primarily at these two things and not at whether you know assembler, Oracle, C++ or .Net. Regardless of the specific technical skills you learned, they will be obsolete before you know it.

To successfully enter the workforce, you really need only one more thing, and based on your question, I suspect that you've got it. You need a burning desire to be more than you are today. Without the drive to grow, your education means nothing. If you've got these three things -- clear thinking, active learning and the desire to grow - you're probably in great shape.

That said, let's take a look at your specific concerns. First, competence. As I've already suggested, don't worry too much about this. Whatever you are going to be hired to do, you've probably never done it before. Your managers will expect you to learn on the job or send you to a class. Entry-level positions pay less than those that require more experience, not because you are young, but because managers expect you to develop your competence and not to arrive with it fully formed.