This is confusing when you've not done it before, I still remember my first time. I thought I'd never get it right. The best part of doing both shoulders at the same time this way is that you don't have to go back and start over and have to decipher the pattern again. You're also less likely to find a glaring error on one side just when you think you were done because you have the mirror images in front of you. Once I got the hang of it, doing both at the same time was the only way for me. It works with sleeves and other things too. You've just gained a valuable skill!
Pat yourself on the back for me, OK?