You're covered in terms of contraception - the 'only protected after a week if you didn't start taking it from day one of your period' is for the first pack. From then on, if you don't miss taking for two days when you're in a middle of a pack or delay starting a new pack for nine days, it works.
So there's no problem in just taking a three day break rather than seven. Whether it will work in terms of spotting, I don't know.