Kik- first of all HAPPY B-DAY!
You've gotten past the biggest hurdle! Really!!! The more your ride alone, the more comfortable you will become with it... the more you ride with traffic, the more used to it you become... which is not to say you take it for granted, but rather you learn how to ride safely with traffic around you...
Absolutely get CO2!!! The tool is cheap, and the refill cannisters are really cheap at WALMART! Like $.99 each... I carry BOTH... A CO2 and a pump... CO2 for ease but a handheld pump in case the CO2 fails or (and yes this has happened..sigh) I have more than 1 flat on the ride. Absolutely go in the garage/backyard or wherever and flat your tire, take it apart, put it back together... practicing in the comfort of your home sure makes it easier when it happens for real...
one more thing... I always put my tubes in a ziploc with some baby powder! Shake it all up (just a little powder to coat the tube) and then when you DO flat, the tube is MUCH easier to slide in as the rubber is coated and doesn't stick to the tire as you try to insert it!!!!!
way to go on tackling your demon... fear! that's a huge hurdle and YOU DID IT!
There is a fine line between "hobby" and "mental illness".