Can you still get pregnant if i missed one day of your birth control but used a condom?

You would need to be ovulating to become pregnant... (that is if any sperm went inside you). The sperm would have to travel up and hit the egg. Condoms act as a barrier to prevent the sperm from hitting the egg. So overall, No you should not get pregnant.

No form of Birth Control is ABSOLUTLY sure (other than not having sex at all). Condoms and birth control pills are each about 99%; if you use both then you are at 99,99 % which is as good as it gets but still not 100%.