I think she's saying the birth control will make your period more regular.
If you are talkign about 3 weeks after taking your last pill I'm assuming that you are still within the regular one month cycle. It would probably take 1-2 months to get back to your "normal" cycle, however even if you miss taking your pills at the regular time by 24 hrs, your doctor will probably always tell you to double up your dose on the next day but still use a backup method of birth control (condoms or whatever) because they can't guarantee that the pill will work. Soo.... within 3 weeks my guess is that you are still safe. But after the next period that you don't take the pill, you are no longer covered.