Step 3: Trouble shooting
Barcodes can be enlarged or shrunk down without it affecting the ability to scan them, so don't worry about distortion. As long as all the bars in the code are in correct proportion, you're good to go.
It would be helpful to cover the barcodes your not using with your fingers so that the scanner doesn't get confused. I will likely go through self scanning checkouts when possible to avoid clerks from freaking out and calling the manager to ask if it's ok to use my card.
Again, below, is the finished product. And I already tried it out at the grocery store and it worked.