What are the chances?

there is a chance you could get pregnant from pre-***. however since you are on birth control you will be aware that it is only about 98% effective. same as a condom. so either way it is the same chances

If you are on birth control and you have been taking it regularly, then you have enough of the pregnancy hormones in your body to prevent you from pregnancy, you should be just fine.

Birth control is designed to prevent pregnancy. taken properly and at the right dose it is about 99'% effective. So you should be fine.

Birth control is generally 95-99% effective, but obviously not 100%. The pull out method also isn't very effective. You likely were exposed to some precum, but the likelihood that you would get pregnancy it very, very low. Your best bet is to use a back up form of birth control if you are nervous or worried.