I also think you're being too hard on yourself. You never would have graduated from nursing school
or passed the nclex if you were as "slow" as you make yourself out to be. You should be proud to be a licensed nurse at the age of 19.
With that said, given that you're
only 19, you're going to have to work extra hard to present yourself as a mature professional. People are going to have a hard enough time taking you seriously. Cut out the "text" talk and slang (no more "I need to c my kid"). Don't show your emotions, keep them bottled up. Don't go to pieces when you make a mistake. Just keep going. Even if you're afraid, don't let it show. Trust me, aides sensing you're afraid is like sharks smelling blood.
In other words, toughen up, or at least give the impression you have. Your problem isn't that you're not "good" enough, it's that you're not assertive enough. Maybe not the advice you want to hear, but it's the best course of action.