Good work! Especially for a self-proclaimed "complete beginner!"
Yeah, your 'left' and 'right' variables most likely override the default left and right variables (I'm not sure how Renpy works exactly). It's a concept in object-oriented programming in which an object can redefine functionality of a parent object. For example, you can define a car with a top speed of 100mph, but then you could define a sport car, which is a car, but it's top speed is 150mph. You should be able to call the overridden variables with super().left and super().right (not sure if it'll work like this in Renpy, but it should in python so ... maybe?). Honestly, defining your own like you said is probably your better option here. You could, say, define 'midleft' and still have the default left, then you could have two characters on the left side, one left and one midleft, without drawing completely new sprites! (good for the 'Hey, my friend here thinks you're cute' situation, maybe?). That's probably way more than you'd ever care to know about that, but hopefully it helps!
Again, great work! Hopefully you feel better too!