I wouldn't risk it, because you just never know. The safest thing would be to use a condom, but if you decide not to, I highly recommend some kind of back-up method. You can use a spermicide or even the withdrawal method, which isn't a reliable method of birth control but is better than nothing. The pill instructions clearly state that you must use back-up for the first seven days, so you should assume the pill is not yet effective. I really urge you to use a condom, but just make sure you use something. I know it can be a pain, but it's not worth the risk.