It happens to people in my office from time to time. So hardly something to be embarrassed about. The check-in agents must see this on a daily basis.

The advice that I always dish out: Check the day of the week for each of your flights. ba.com is good at showing them on every screen. It's not foolproof (Feb/Mar is a particularly bad error for being hidden and therefore untrapped), but most of the time it should immediately ring alarm bells if the day of the week displayed is not the day of the week you're expecting to travel on.