Missed a day last month...

Ok so I'm on the pill and I'm pretty good at taking it every day at the same time to make it more effective. Last month, however, I forgot to Tia it one day but the rest of the month I took every single one without missing another. Tomorrow I'm starting the new packet and also have plans to have a little fun :p and of course a condom will be used anyway but in the event that we don't use one, will I still be ok and not get pregnant? Or should I get the plan B?