How effective is bithcontrol??

Madison
How effective is birth control? I hear doctors say it works 99.9% of the time but I have heard so many stories and even have friends who now have babies who were on birth control. IV been taking mine for about 4 months and my S/O no longer pulls out. I take it every day at the same time maybe 5 mins off. Should I worry about possibly becoming pregnant? Should I take more precaution?