Does pre-cum get a girl pregnant? Does taking a shower after penetration prevent conception?

You can't get pregnant through anal.

This is not a really but the same happened to me

Your penis is too small to impregnate a woman.

Penis size has nothing to do with getting someone pregnant, as long as you produce healthy semen even if it only reaches the vagina entrance pregnancy is possible.
Just because your the one who seems to have a small penis don't go around making false accusations against other people!
Grow up and get an adult life instead of doing childish trolling actions!

You are very likely to get pregnant if here is sperm inside you when you ovulate (usually 14th day after your period starts. Showering wll not wash semen out (well, not all of it!).
Maybe you are infertile or your coitus did not happen at the right time of your month

There is no guarantee that the fluids you refer to as "pre-cum" (that is not what they are) do not have sperm in them. Taking a shower will not help but washing deeply inside the vagina which is known as a douche, may reduce the odds of becoming pregnant - it is not a guarantee. It is not just washing but a flow of water into the vagina. Why not always carry protection with you or encourage your girlfriend to get fitted for a diaphragm or an IUD? When I was a teen I practiced pulling out before coming - a foolish thing to do, known as coitus interruptus. Luckily my girlfriend never got pregnant. We had wanted to marry but it still would have been extremely difficult for her to have been pregnant at our age. Part of me wanted her to be at that time and thought it would be so cool to be only 15 years older than my child. I guess I will never know what that might have been like. Looking back I now know that I wasn't ready to be a parent and also that her parents would have had too much control of our kid and of us.