Setting aside the "be yourself" stuff for a moment, I think the main issue with your look as shown in your photo is it's neither here nor there. Your look is neither rough around the edges nor fashionable enough to say "rock & roll". Look at the pics people have posted here - they're either more grungy and tough looking, or way more stylish and daring than your look. Lemmy is grungy looking, McCartney & Deacon are stylish, Bolan is flamboyant - all of that is rock & roll. But you're just safely somewhere in the middle, not much of anything. The safe all-black look, the club shirt, the little subtle necklace, the nice bass, it looks like well-to-do kid playing trust fund equipment. Everything's well-mannered but nothing stands out. There's no theatrical quality to it. You look like an audience member, not a performer.
I think the answer is to be more of anything. You don't have to grow your hair long or get tattoos or wear a certain kind of clothing. You just need to move demonstrably in some direction away from center, some direction that makes some kind of statement. For example, something as simple as a jacket can make a difference - take the look you have in the pic and add a sportcoat, and then under that a loosened tie, or an opened shirt with more showy necklace, or a cool band t-shirt, and just like that you've made an easy and noticeable step in a more R&R direction. But that's just a random example. You don't need to dress like Bootsy, you just need more of something. It's hard to make yourself look poor while holding a StingRay, so you may be best off going in a slightly more fashionable direction; not high fashion, but something in the Stones direction, maybe. And definitely tousle your hair. It doesn't have to be long or crazy, but yours is too neat and tidy. Lose the part, for a start.
I'd also suggest avoiding two R&R cliches: don't get any tattoos and don't take up smoking. No tattoos, because you will change as a person with time, and a tattoo will just be a permanent monument to what you thought you knew when you were young. Trust me, life will give you plenty of reminders of how clueless you were at this age without need for a printed reminder in the mirror each day. You may be health-aware enough to already avoid smoking, but it will cause long-term issues to you and the people around you (everyone via 2nd-hand smoke, and your loved ones in dealing with the future health issues).
Good luck deciding what kind of R&R you want to be, and being it more forcefully!