Mo, it's not so unheard of for people your age to have root canals, it's just not spoken of quite as often. I had my first root canal done when I was either 14 or 15 (It's been roughly ten years). Sometimes you can take perfect care of your teeth and still wind up needing a root canal for various reasons - They are nothing to be ashamed of! You have just 2 amalgam fillings and one root canal?? Good lord, your teeth are in an infinitely better state than mine - I think at this point, I've racked up a filling in nearly every tooth in my mouth, three crowns, a bridge, and four root canals. The point of all of this being done at young(ish) ages is so that when we ARE older, our teeth won't be terribly decayed or missing. Think of it this way: It's so much better to nip this in the bud while you're young and willing to change your dental habits.
As far as being frightened of the root canal, it's not nearly as bad as movies and TV make it out to be. Your dentist should wait until you're good and numbed before he does anything (and chances are, you won't even really feel the injection of the numbing meds). Honestly, the worst part of my latest root canal (done in April) was trying to keep my mouth open and when I mentioned it, the dentist put in a bite block (a piece of rubber) that I could rest my teeth on and take the pressure off of my jaws.
Good luck!!