Low, but there's still a chance. The statistics say you have about 92%-99% chance of not getting pregnant. That mean that about 1-8 women out of 100 get pregnant on The Pill each year. Planned Parenthood - The Pill

However, you're saying that you had him pull out for the first three months. While this reduces your chances of getting pregnant, the withdrawal method (which is what that's called) is not an effective birth control method, because most of the time, there's pre-ejaculate on the tip of his penis at some point before he ejaculates.

It's important, of course, to take the pill not only every day, but at the same time. If you should miss a pill, your gyno should have given you instructions for that, but always use a backup method for that month as well.