Sammuel:
Jamie's post is really good and I second the recommendation that you read it.
With that being said, I'm going to ask what I think is the most important question: Should you be charging for performing?
I'll start by saying that I have never seen you perform and have no idea how good a performer you are. But let me ask some questions which will help you decide whether you should be charging for your performance:
1. Do you have an act? For walk-around, that means having at least three sets of three effects that are scripted and presented in a coherent entertaining manner -- it doesn't mean that you have three tricks that you perform while narrating what you are doing (I put this card here, and then it does this). For other performances, it means having a show that is scripted and presented in a coherent and entertaining manner. Let me expand a bit on three of the words I've used:
Scripted - This means that you have thought about, written, revised and rehearsed what you are going to say. Although you have a script, it comes across as if you are just having a conversation with your spectators (not like you are reading Shakespeare) and has an impromptu feel to it. The script should reflect your performing style whether it is funny, sarcastic, serious or bizzare.
Coherent - This means that there is a reason that one effect is placed after another. It includes having effects that draw the audience in, effects that showcase strong magic, effects that provide a laugh and provide a strong ending to the routine or show but having those different effects tied together in a way that makes sense.
Entertaining - This means that YOU are entertaining the audience by presenting the magic. As magicians we are entertained by the magic, but lay people are entertained by the magician. Reread that last sentence and think about it. This is the most important thing about being a "professional." Being entertaining means that your patter needs to be more than say-do-see patter where you say what you are going to do, do it and then tell the audience to see what happens (if you find yourself saying "waaaaatch" in a deep voice for every effect - they you likely are using say-do-see patter). Eugene Burger calls that type of presentation "the adventures of the props in the magician's hands."
2. Is your magic flawless? Have you practiced it and performed your effects so that there is nothing that can go wrong? Have you performed the effects enough times that anything that you have a solution for everything that could go wrong? Is your presentation confident and consistent - does it seem like you are making things up as you go and trying to think of what you are going to say or does your presentation have a professional feel to it being delivered flawlessly?
3. Do you use a variety of props and a variety of presentations? Or are you just doing one find-a-card trick after another? Does you show have texture to it in that the presentations for each effect are varied?
4. Can you effectively handle difficult spectators and hecklers (there is a vast difference between the two)? Do you have the experience to know when to ignore them, when to engage them and how to handle them?
5. Do you look like a professional? I'm not talking about your physical attributes, but more so how you dress and how you handle yourself.
With you being 13, you need to be twice as good as someone twice your age.
Maybe a simpler questions would be: "Do you think you are worth $100 for an hour?" Put another way, do you realistically think someone would pay $100 an hour to hire you? If not, then you are not ready to get paid for your performances. I think that $100 an hour is the low end of what a magic show should cost. If your show isn't worth $100 for an hour, you shouldn't be charging.
Realize that I'm not saying this to discourage you, but to keep your expectations in line with reality. You are young and you have lots of time to perfect your magic so that when you are 18 you will be able to charge $200 an hour for a show. Take your time and perfect the art. Learn as much as you can by reading Tarbell rather than buying the trick of the month. Read books on presentation. Learn about the history of magic. Get as much performing experience as possible. Develop routines and shows that demonstrate your talent and creativity. Practice, rehearse, perform and (as Draven says) repeat.