I see that there are a ton of responses and this might have already been suggested, but have you thought about bringing it back to the place that has done your oil changes in the past. Have them do one last change and make sure that you tell them not to over-tighten the bolt. Test that the bolt moves afterwards and then you will be set for oil changes in the future. As for the supplies that you have bought - either return them to Autozone or just hold on to them for a few months and use them for the next oil change.
Hey Julia! A inexpensive torque wrench can be purchased at Wal-Mart for under $50, the correct amount of torque on a lug-nut is 80lbs. It's a shockingly low torque requirement. Put more than that and you're risking breaking the stud. I know because I snapped a rear stud when I was rotating my tires. I didn't have a torque wrench and just threw caution to the wind... I thought the same thing, I'll just tighten it down and everything will be okay... yeah not this time! I was able to replace the stud myself but I didn't like driving anywhere with that lug nut missing! I highly recommend the torque wrench if you are going to be changing or rotating your own tires. Here's a link to a youtube video on how to use a torque wrench:
Hey, Daves09Prius! Thanks for the helpful post and the really great video! I appreciate it very much. Julia