Well, you are. No, seriously, this is a typical problem in most cultures around the world. People tell their children (with words and actions) that they are no-good, worthless, useless drains on their parents' happiness, pocketbooks, and patience. Given this scenario, you get a lot of adults who became convinced as children that they were just no good, and they helpfully pass this attitude on to their children. Lovely predicament, eh?
Well, thankfully, they were wrong. Let's take useless first, it's easier. You cannot be classified as useless, because you aren't really supposed to have to make yourself useful. Look at the natural world. What is the use of a tree? Well, it has many uses, but it isn't TRYING to be useful. There's the difference. It's just doing what it wants (or so we assume) and in the process of doing that it does its job in the natural order of things. Despite all the rantings of moralists, you are in the same boat. The only way you are ever going to do an ounce of good in the world is to do what you want. Do what makes you happy, or at least what distracts you from your misery. Important Note: If you have an underdeveloped sense of empathy and enjoy doing things that harm others, ignore this advice and get professional help!
How, you may ask, does doing what you like do any good? Look around you. Look at people who seem to be trying very hard to be useful. Are they really doing good things for people? Or do they make everyone around them miserable with all their moral uppidyness and incessant busy bodying? I suspect it is the latter. The people who really do others some good are the people who are doing what they like and who aren't very interested in being useful. They are usually interesting to be around, because they are doing things that interest them. They are often fun to be around, because they appreciate fun and know how to laugh and not take anything too seriously. They inspire other people to figure out what it is that they want to do by example, thus causing more people to be interested in life and interesting to be around, fun loving, etc.
Out of all the people we meet in life, these people who are doing their own thing are the people who have the most profoundly positive impact on us and thus make our lives richer in the most fundamental, meaningful way. Can you really call that useless? Sure, working in a soup kitchen will feed people, but if you're being a martyr about it because you don't really want to be there, everyone around you will see right through you and hate you for being moralistic and insincere, and you will end up doing more harm than good. So, revel in your perfect uselessness. It's the useful thing to do.
What if everyone in the world just did what they wanted? Would it be anarchy? Well, that starts to get into the subject matter for our eventual companion page, How to Solve All the World's Problems.