If you have cotton yarn, wash cloths are great to practice tension on too. You can wash your face or dishes with something imperfect, they don't care, and you'll have something smaller that you can bind off and say, "I knitted it myself!"
I should never overestimate my basic arithmetic skills.
Cheating is an option. . . . Cheaters never win and winners never cheat, but smart knitters who want to retain an iota of sanity do, cheerfully. ~~Kory Stamper